An exhibit is an item that is shown off for the public, such as a painting on display at a gallery or a historical document shown under glass at a museum.
The main thing to remember about an exhibit is that it refers to something presented formally and in a public setting. For example, if you put an action figure on a side table in your apartment and your friends come by and notice it, well, it’s just an action figure on a side table. Put that same action figure on a pedestal in a fancy gallery, arrange it just so, and voilà! It’s an exhibit. People may even look it over and discuss its meaning in hushed tones. Students of law — or people who watch a lot of TV — will know that when used in a legal context, the word exhibit can also refer to an item presented as evidence in a legal court.