A prospect can be in or out the campaign.
A prospect can have 4 different statuses in a campaign.
In campaign: Prospects for whom the campaign is running. Prospect is still receiving the steps of the campaign.
Out of campaign:
Exited: Prospects for whom the campaign was stopped because they performed an action that triggered an exit, e.g. they replied, clicked a link, qualified or converted
Completed: Prospects who went through all the steps of the campaign and did not trigger an exit event
Removed: Prospects for whom the campaign was stopped manually. The prospect has been removed from the campaign.