# Ob

**Objective**- The optical element which receives light from the object and forms the first or primary image in telescopes, microscopes and other optical systems.
**Objective Tinnitus**- This refers to abnormal or pathological sounds originating within the body, in the region of the ear, which are audible to others than the subject.
**Oblate Spheroid**- An ellipsoid produced by rotating an ellipse through 360° about its minor axis.
**Obligate Anaerobes**- An organism that dies when exposed to oxygen.
**Oblique Angle**- An angle that is not a right angle.
**Oblique Coordinates**- A coordinate system in which the axes are not perpendicular.
**Oblique Triangle**- A triangle that is not a right triangle.
**Observation**- Observations refer to repeated values of a data variable. The rows of a column represent the observations.
**Obsidian**- A black or dark-coloured volcanic glass, usually composed of rhyolite.
**Obtuse Angle**- An angle larger than 90° but smaller than 180°.
**Obtuse Triangle**- A triangle that contains an obtuse angle.