What does the expression "that old chestnut" mean and what are its origins?

It's an "old saying" or truism, especially if it's overused or trite.

What does the expression "that old chestnut" mean and what are its origins?
I come fron a fishing town that used to be full of rough-ish fishermen many many years ago(40yrs).Funnily enough someone asked me today where I was from and came out with "is it still full of rough fishermen", and your question is exactly what I replied.
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Reply:The age of a chestnut tree and Jimmy Tarbucks jokes.