what is "other" listed on the flash drive storage

I'm trying to clean up my computer and remove old files to free up space. When I look at the flash drive storage, a category "other" shows to be taking up a majority of the flash drive space. This is listed along with "photos", "movies", "backup", etc. What is "other"? If I could figure out what "other" is I could go to that area and potentially delete unwanted files to free up more memory. Any advice?