A tracked user is anybody who posts, votes, or comments in your Canny boards. Once tracked, a user can post, vote, or comment as many times as they want—they will only ever count as one user.
Note that users you "vote on behalf" of are counted as tracked users as well.
Does it reset every month?
No, as long as the user is in the Canny system, they are a tracked user.
Can I delete tracked users?
Yes, as a Canny admin, you can delete tracked users. Read more about that here.