When to use a comma before "or":
* In a series of three or more items:
* "I like apples, oranges, or bananas."
* "She went to the store, bought groceries, or visited her friend."
* When "or" connects two complete sentences:
* "We could go to the movies, or we could stay home and watch TV."
When to NOT use a comma before "or":
* When "or" connects two words or phrases:
* "I want coffee or tea."
* "She went to the beach or the mountains."
The key: The comma helps to separate the items in a list, or it indicates a pause between two independent clauses. It's not used just because the word "or" appears.