There are different Usages of the letter P.
1. the sixteenth letter of the English alphabet
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
This letter denotes the next after O in a set of items, categories, sizes, etc. e.g. It also denotes the sixteenth of sixteen or more hypothetical people or things.
P = Parking as on roadside signs. p = para as in p-xylene.
Besides, P letter of the English Alphabet is used in Portugal as the International Vehicle Registration.
In Chemistry P = Phosphorous the 17th element of the periodic table. p=pico as in the unit of measurement, 1pm = 1 10-12 m
The most Common Noun which is used to learn this letter at the Nursery level is Parrot; P for Parrot.