Hey, I'm just wondering what "hits" is referring to here in my library?

Hits means someone from the network is hitting on your shared files if thats not what you're referring to then you'll have to be a tad bit more specific.

ie: it means how many times each file you're sharing has been found in someone else's search. If the file has tags such as id3 tags then it may relate to that (accurately or inaccurately depending on the words used within the descriptive tag.)