Pm

Pm
Promethium is a radioactive element of the rare earth series.
PM0.1
Ultrafine particles.
PM10
Particles measuring 10µm or less.
PM2.5
Particles measuring 2.5µm or less.
PMC
Abbreviation of Polymer Matrix Composite.
P-MOSFET
In a MOSFET device the gate is insulated from the channel by a very thin (typically less than the wavelength of light) layer of glass (silicon dioxide) and the gate is either metal or doped silicon (polysilicon), hence the acronym metal-oxide semiconductor.