English

Well you can say    

John is playing.                       "John" is a noun.

He is playing                          "He" is a pronoun

A pronoun can be used in place of nouns.

Pronouns are words like     he,she, it, him, her, ..

I just found this.

It is the same for numerals and pronumerals.   Pronumerals (letters) can be used in place of a number.

for example in the maths expression     5y        y is a pronumeral.