Peak level
The maximum instantaneous amplitude of the wave (e.g. sound pressure).

Phon
The phon is a unit of perceived loudness, which is a subjective measure of the strength (not intensity) of a sound. The phon value of a given sound is the sound pressure level in dB of a 1000 Hz sound, which is perceived as loud as the given sound. E.g. if a given sound is perceived to be as loud as a 60 dB sound at 1000 Hz, then it is said to have a loudness of 60 phons.

Pink noise
Pink noise is a noise containing equal power per octave band.

Plenum
In suspended ceiling construction, the space between the suspended ceiling and the main structure above or analogue for a raised floor the space between raised floor and main construction. The acoustic properties of the plenum influence the sound propagation in the building and the room acoustics in the room.

Porous absorption
Sound absorption in a porous material like Rockwool wool caused by
friction between air movement and the material (e.g. fibres). Other forms of absorption can be based on wave interference in Helmholz absorbers or membrane absorbers.

Pure tone
A pure tone is a sound which only contains one single frequency, the wave form is a simple sine wave (sine tone).