"Other" Storage space in Sys Info
"Other" is all the files on your drive that aren't Audio, Movies, Photos, Apps, or Backup; in other words, all your documents and other saved files (and any media files in a format that System Information doesn't recognize as media files).

If you want to determine what files are taking up a lot of room on your drive, a tool like OmniDiskSweeper (free from OmniGroup) can help you identify where and what the files are that are taking up large amounts of space on your drive. Note that you might end up wanting to "clean it up" and you might discover that the space is taken up by files that you value and want to keep.