| Noun | 1. | red flag - a flag that serves as a warning signal; "we didn't swim at the beach because the red flag was up"signal flag, flag - a rectangular piece of fabric used as a signalling device | |
| 2. | red flag - the emblem of socialist revolution | |
| 3. | red flag - something that irritates or demands immediate action; "doing that is like waving a red flag in front of a bull" | |