The different options under Inbox are designed to have an overview of your actions/pending actions for your Matches.
Interest received: Members who have expressed interest in your profile & pending action from you. You have an option to accept or decline the request.
Accepted: Both you & your match mutually liked each other and want to take it further.
Interest sent: Profiles you liked & to whom you had sent an invitation.
Contacts viewed: List of contact numbers viewed by you post buying a premium membership.
Declined/Cancelled: List of the profiles whom you have declined or declined by your matches on an interest sent.
Filtered out: Interest received from Filtered Out Matches (as set in Contact Filter).