1. Apartment: This is the most common meaning. A "flat" is a self-contained residential unit, usually on one floor of a larger building. It's similar to an apartment in American English.
2. Tiresome or boring: Someone or something can be described as "flat" if they are dull, uninteresting, or lacking in energy. This meaning is similar to "blah" or "uninspiring" in American English.
3. Broke: "Flat broke" means having no money.
4. Completely: Sometimes "flat" is used to emphasize a degree or intensity. For example: "He refused flat." This means he refused without any hesitation or qualification.
5. Flat out: This means "completely" or "without hesitation." For example, "I was flat out exhausted."
6. Flat chat: This phrase means "to talk incessantly," especially about something trivial or insignificant.
7. Flat to the board: This means "completely flat." It's often used to describe something that has been completely deflated or has lost all its air.
The specific meaning of "flat" will be clear from the context of the sentence.