How do you denote A or B?

A or B is also called A union B and is often shown using the notation:

(A U B) meaning A Union B meaning A or B

You denote "A or B" as P(A U B)

You denote "A and B" as P(A n B)

AUB - A Union B. This could also be shown via a Venn diagram.

Assuming this is about 2 independent events in probability: A or B can be denoted as "A union B" where the 'union' bit is written as a U. So it would be often written as "A U B". This can also be shown visually on a venn diagram by shading in any area that lies within circle A or within circle B.