What does a mean in British?

"A" in British English is the same as in American English - it's the indefinite article, used before singular nouns when you're not referring to a specific one.

For example:

* "I need a pen." (Any pen will do)

* "She bought a new car." (Any new car, not a specific one)

However, "a" can also be used in British English as a slang term, similar to "very" or "extremely."

For example:

* "That was a good film!" (meaning "That was a very good film!")

* "I'm a tired." (meaning "I'm extremely tired")

This usage is more common in informal speech and might not be understood by everyone.

It's important to note that the "a" in this slang usage is often pronounced with a stronger emphasis than the regular indefinite article.

If you're unsure about the context, it's always best to ask for clarification!