A prospect can be active or archived.
An active prospect (or un-archived prospect) is a prospect that is available to be contacted, to be added to a list, to be added to a campaign, etc.
An archived prospect is a prospect that cannot be contacted, cannot be added to a list and cannot be added to a campaign. It is a prospect that we don't need anymore.
If a prospect is asking you to never be contacted again, please archived him. However, if he/she wants you to remove all data you have about him/her, you have to blacklist him.