P

Pallet -

Part of the escapement and shaped something like a ship's anchor.
        
 

Patina - discoloration due to age

Perlage - a surface decoration consisting of a pattern of overlapping dots.

Pedometer - a device that counts the number of strides taken by the wearer.

Perpetual Calendar - a calendar complication that adjusts automatically for different month lengths and leap years.  Perpetual calendars are programmed to be accurate until the year 2100.

Pinion - 
            Toothed wheel usually made of steel with a small number of teeth. 
                   (see Wheel)
 
           
Plate -

A piece supporting the various parts of the movement and the bridges. The bottom side of a plate is the dial side, the top side is the bridge side.
            

Platinum - One of the rarest of precious metals as well as one of the strongest and heaviest. Platinum has a rich, white lustre and is hypoallergenic and tarnish resistant.

Plexiglas a clear, lightweight type of plastic. Plexiglas, as you would expect, is the least expensive. It is also the least likely to shatter and the most likely to become scratched.

p.m. - post meridian (after noon). From the latin post - after, medius - middle, 
diem - day.

Pointer Calendar - a hand points to the date as opposed to  the date appearing in a window.

Power reserve indicator -

a subdial used to show how much power remains before the watch stops running.
                                        

Pulsometer - Scale on the dial or bezel of a watch that works in conjunction with the seconds hand to measure pulse rate. A reference number tells how many pulse beats to count. 
e.g. If the reference number is 15, the operator counts 15 pulse beats. At the last beat the seconds hand shows the pulse beat per minute.

Pushers - see Buttons