 Purpose
Test multiple conditions with OR

Return value
TRUE if any arguments evaluate TRUE; FALSE if not.

Arguments
logical1 - The first condition or logical value to evaluate.
logical2 - [optional] The second condition or logical value to evaluate.

Syntax
=OR(logical1, [logical2], ...)

Examples
For example, to test if the value in A1 OR the value in B1 is greater than 75, use the following formula:
=OR(A1>75,B1>75)
OR can be used to extend the functionality of functions like the IF function. Using the above example, you can supply OR as the logical_test for an IF function like so:

=IF(OR(A1>75,B1>75), "Pass", "Fail")
This formula will return "Pass" if the value in A1 is greater than 75 OR the value in B1 is greater than 75.

Array form
If you enter OR as an array formula, you can test all values in a range against a condition. For example, this array formula will return TRUE if any cell in A1:A100 is greater than 15:

=OR(A1:A100>15)
Note: In Legacy Excel, this is an array formula and must be entered with control + shift + enter.