The lowest temperature at which a substance will begin to burn; combustion point.

Literally "a cotton shop on fire," this is a punning expression meaning there is nothing left to talk about. The pun relies on the word [[谈|談|tan2]] sounding like [[弹|彈|tan2]]. If the cotton shop burns down, there is no more cotton to fluff, hence "no [[弹|彈|tan2]]" is used to mean "no [[谈|談|tan2]]."