OR is a Boolean operation which will be true when any of its inputs are 1. That is (on a two input gate) when one input, OR another, OR both are true - the output is true.
Consider the truth table for this:
| Inputs | Output | |
|---|---|---|
| A | B | C |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
