In Prospect.io, by default, a prospect is Active.
An active prospect is a prospect that is available to be contacted, to be added to a list, to be added to a campaign, etc.
If you don't want to contact a prospect anymore, and you don't want it to appear in the application anymore, you can archive them.
View archived prospects
When a prospect is archived, you won't see them on the prospects screen anymore. You can display archived prospects by clicking the View archived prospects link on the top of the screen:
Difference between Archived and Deleted
You can also choose to delete a prospect. The main difference is that if you delete a prospect, they will completely disappear from your account and you'll loose all associated data (emails, replies, etc.).