what does "cheers" mean when the British says it?

问题描述:

what does "cheers" mean when the British says it?
They British say it so often.Is there other meanings other than the word you say when making a toast?
Sorry,but it's actually a question,not an English to Chinese task...
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they say it when there's something to cheer about?obviously.Like,"cheers mate!" or it's so often used sarcastically,like when i say it^^
you seem to know english for real,where you from?