Other is all of everything on your computer.
One thing you could do is:
1. Open System Preferences
2. Open Spotlight
3. Press on the Privacy tab
4. Drag you Macintosh HD into the Privacy plane
5. Restart your computer
Then repeat the process, except this time (in the Privacy tab) click on your Macintosh HD and click the minus
( - ) to remove the Macintosh HD from the Privacy tab. Close System Preferences and open Spotlight (magnifying glass) and wait for the HDD to be re-indexed.