What is "punchbag"

Usage examples of "punchbag".

At some point Mercy seemed to have moved all of her substantial amounts of possessions into my bedroom, her underwear and her stuffed toys and her punchbag and her weights.

Or had he been freelancing, summoned here only as a punchbag, but stealthy enough to bring a hidden camera with him?

At least in the next war there won't be any special wimps, punchbags, or unpopularity contests.