Is or a pronoun

No, the Word 'or' is a preposition, a Word used to join alternatives; used to introduce a synonym or explanation; used to introduce a consequence.

Examples:

I'm not sure if I should get the redor the blue.

I haven't checked my emails, ormessages, yet.

Watch your account balance or you could overdraw.

A pronoun is a Word that takes the place of a noun in a sentence.

Example: Jack will be here by six, or sooner, if he can get the early train. (the pronoun 'he' takes the place of the noun 'Jack' in the second part of the sentence)