Extreme value of a varying quantity, measured from the zero or mean value.
Peak Counting
This method identifies the occurrence of a relative maximum or minimum load value.
Peak Current
The maximum current that flows during a complete cycle.
Peak Hold
The peak signal level for each frequency component is held for display.
Peak Load
The maximum demand for electricity from an electrical system in a given period of time.
Peak Pick
A parameter estimation technique where the peak value of the imaginary part of the frequency response function is used to estimate the mode shape value at that point.
Peak Sound Pressure Level
ten times the common logarithm of the square of the ratio of the largest absolute value of the instantaneous sound pressure in a stated frequency band during a specified time interval to the reference sound pressure of 20 micro pascals.
Peak to Average Power ratio
Usually expressed in decibels and used to determine the robustness of a modulated signal against nonlinear distortion.
Peak to Peak Value
The over-all amplitude of a signal measured from its lowest peak to its most highest peak.
Peak Torque
Maximum amount of torque an engine can produce.
Peak Value
The instantaneous maximum value of a waveform.
Peak Voltage
The maximum value present in a varying or alternating voltage.
Peaking Coil
An inductor used in an amplifier to provide high-frequency compensation, which extends the high-frequency response of the amplifier.
Pearl Ash
An old fashioned name for Potassium Carbonate.
A lamellar aggregate of ferrite and cementite.
Pearson Product Moment Correlation Coefficient
A dimensionless index that reflects the extent of a linear relationship between two data sets.
Partially carbonized vegetable material, usually found in bogs.

Equal to two to the power of fifty bytes.
An old unit of volume.
Peclet Number
A dimensionless number that is the ratio of heat advection to heat diffusion.
Pedal Triangle
The pedal triangle of a point P with respect to a triangle ABC is the triangle whose vertices are the feet of the perpendiculars dropped from P to the sides of triangle ABC.
Pedestal Bearing
A bearing that is supported on a column or pedestal rather than on the main body of the machine.
In a classical-style building, the triangular segment between the horizontal entablature and the sloping roof.
Peel Strength
Strength of an adhesive bond obtained by stress applied in a peeling mode.
Peen Hammer
A body hammer with a pein of triangular section with a fairly sharply shaped end.
The mechanical working of metals by means of hammer blows.
Peer to Peer
A network operating system where any device on the main network bus can initiate communication.
Peierls Stress
The stress required to move a dislocation.
Pein Hammer
A body hammer with a pein of triangular section with a fairly sharply shaped end.
Pell Number
The nth term in the sequence 0, 1, 2, 5, 12,... defined by the recurrence P0=0, P1=1, and Pn=2Pn-1+Pn-2.
Peltier Effect
The change in temperature produced at a junction between two dissimilar metals or semiconductors when an electric current passes through the junction.
PEM Fuel Cell
Abbreviation of Proton Exchange Membrane Fuel Cell.
Pencil Beam
Emission, from an antenna, having the form of a narrow conical beam.
A curved support shaped like an inverted triangle, used to support a dome.
There are a number of different forms of pendulum. The main characteristic being that when the mass is displaced from it's position of rest it will oscillate at a fixed frequency.
penetrant inspection
A method of nondestructive testing for determining the existence and extent of discontinuities that are open to the surface in the part being inspected.
An old unit of mass equal to 24 grains.
Penrose Impossible Staircase
A four sided staircase that always goes up if you travel around it in one direction and always down if you travel in the opposite direction.
Penstock Valve
A type of simple gate valve, used to contain fluids in open channels and often found in waste water treatment plants.
A period of 5 days.
A 15 sided polygon.
Pentafluoride Antimony
Alternative name for Antimony Pentafluoride.
A polygon with five sides.
Pentagonal Number
A number of the form n(3n-1)/2.
A star shaped figure constructed by extending all of the sides of a regular pentagon until they meet at the points of the star.
Pentagrid Converter
A five-element tube employed as a mixer-oscillator in superheterodyne receivers.


The fifth member of the paraffin series. Pentane exists in three isomeric forms.



A colourless liquid at room temperature with a choking aroma.

Pentavalent Impurity
A type of impurity that contains five valence electrons and donates one electron to the doped material.
Pentode Tube
A five-electrode electron tube containing a plate, a cathode, a control grid, and two grids.
A five-square polyomino.
The transition region between the darkest shadow and full brightness.
An enzyme that hydrolyzes a peptide bond.
A short polymer made by linking together amino acid molecules.
Peptide Bond
A planar, amide linkage between the α-amino group of one amino acid and the α-carboxyl group of another, with the elimination of a molecule of water.
per annum
A traditional unit of frequency equal to once a year.
Per Diem
A traditional unit of frequency equal to once a day.
per Foot Run
A unit of measure in woodworking where the only dimension of concern is the length. The width and thickness are not included in the calculation.
per Foot Super
A square foot of wood of any thickness.
Per Mensem
A traditional unit of frequency equal to once a month.
per mill
Parts per Thousand
Perceived Colour
Also known as visual colour is the quality of light emission as conveyed by the human eye, combining the impressions of 3 types of light-sensitive cells which the eye contains.
Perceived Noisiness
The metric for Perceived Noisiness turned out to be far less robust than the metric for Loudness. It was an early indication that the acceptability of a sound was product specific to a certain degree.
A ratio that compares a number to one hundred.
Percent of Modulation
The degree of modulation defined in terms of the maximum permissible amount of modulation.
Percent Yield
Equals experimental yield divided by theoretical yield times 100%.
Percentage Articulation Loss of Consonants
Estimate of speech intelligibility.
A value on a scale that indicates the percent of a distribution that is equal to it or below it.
Perceptual Coding
A lossy form of coding where parts of the signal that are not perceptible to the end user are removed.
Perfect Crystal
A crystal with no defects or impurities, made of completely identical repeating subunits.
Perfect Cube
An integer is a perfect cube if it is of the form m3 where m is an integer.
Perfect Fluid
A fluid chiefly characterized by lack of viscosity and, usually, by incompressibility.
Perfect Gas
A gas that obeys the ideal gas law.
Perfect Number
A positive integer that is equal to the sum of its proper divisors.
Perfect Power
An integer is a perfect power if it is of the form mn where m and n are integers and n>1.
Perfect Radiator
A Black Body radiator.
Perfect Square
An integer is a perfect square if it is of the form m2 where m is an integer.
By-products of aluminum smelting and uranium enrichment. Also replace chlorofluorocarbons in manufacturing semiconductors.
Alternative name for Tetrafluoromethane.
Perfluorosulphonic Acid


Most commonly used electrolyte in a Proton Exchange Membrane Fuel Cell.

The point of an orbit nearest to the centre of attraction of an orbiting body.
The point on a spacecrafts orbit at which it is nearest to the centre of mass of the system.
That point in the trajectory of a vehicle which is closest to the moon.
Another name for Acenaphthene.
The point of a satellite's orbit closest to Earth.
Perigee Speed
The speed of an orbiting body when at perigee.
Perihelic Opposition
When the Earth passes between a planet and the Sun when the planet is at its closest from the Sun.
The point of closest approach for any object orbiting the sun.
The distance around the outside of a shape.
The time taken for a full cycle of motion in a system executing harmonic motion.
A term used to refer to a pattern of motion which repeats exactly after a given interval or period.
Periodic Law
The properties of the elements are periodic functions of their atomic numbers.
Periodic Quantity
Oscillating quantity whose values recur for certain increments of the independent variable.
Periodic Table
The most commonly used arrangement of the periodic system.
Periodic Trend
A regular variation in element properties with increasing atomic number that is ultimately due to regular variations in atomic structure.
Periodic Wave
A waveform that undergoes a pattern of changes, returns to its original pattern, and then repeats the same pattern of changes.
Peripheral Component Interconnect
Standard for PC expansion cards - more commonly known by the abbreviation PCI.
An isothermal reversible reaction in metals where a liquid phase reacts with a solid phase to produce a single, different, solid phase upon cooling.
An interpreted language optimised for scanning arbitrary text files.
Perennially frozen ground that occurs wherever the temperature remains below 0°C for several years.
Permanent Hardness
Water hardness that remains after boiling the water, mainly due to dissolved calcium sulphate.
Permanent Magnet
A magnet that retains its magnetism after removal of the magnetizing force.
Permanent Magnet Speaker
A speaker with a permanent magnet mounted on soft iron pole pieces.
Permanent Threshold Shift
A permanent decrease of the acuity of the ear at a specified frequency as compared to a previously established reference level.
Permanganic Acid
Alternative name for Manganese VII Oxide.
Permangante of Potash
Old fashioned name for Potassium Manganate VII.
  1. passage or diffusion of a gas, vapor, liquid, or solid through a material without physically or chemically affecting it.
  2. Term used to express various relationships between magnetic induction and magnetizing force; either absolute permeability or specific (relative) permeability.
Permeability of Free Space
μ0 = 4πx10-7 Hm-1
The property which determines the magnitude of magnetic flux in a material.
The geological period from 290 million to 245 million years ago.
The proportionality constant between the dielectric displacement D and the electric field E.
Permittivity of Free Space
ε0 = 8.85419x10-12 Fm-1
Permutations and Combinations
A permutation is a particular sequence of a given set of objects. A combination is the set itself without reference to order.
At right angles to. A line at right angles to another line or to a plane.
The length of time a phosphor dot glows on a CRT before disappearing.
Personal Computer Memory Card International Association
An expansion bus architecture which is the de facto standard for notebook and laptop computers.
A feeling of depth.
Perspective Drawing
A drawing in which, in order to show perspective, oblique parallel lines will meet.
Tradename for Polymethyl Methacrylate Resin.
A chemical or biological agent that kills pests.
Prefix representing a multiplication of 1015
One quadrillion (1015) floating-point operations per second.
A volatile, flammable liquid mixture of hydrocarbons, obtained from petroleum and used as a fuel for internal-combustion engines.
Petrol Engine
An internal-combustion engine in which the fuel is petrol that is drawn or injected into the cylinder along with air and ignited with an electric spark.
An oily, thick, flammable, usually dark coloured liquid that is a form of bitumen or a mixture of various hydrocarbons, occurring naturally in various parts of the world and often separated by distillation into petrol, naphtha, benzene, kerosene and paraffin.

Petroleum Fuel
Petrol or diesel fuel.
Peukert Equation
A formula that shows how the available capacity of a lead-acid battery changes according to the rate of discharge.
Tin-base white metal containing antimony and copper: 1 to 8% Sb and 0.25 to 3% Cu.