Hi Rajan,
A suppression list is a list of subscribers that you don’t want to receive your communications. Suppression lists filter out email addresses and prevent those addresses from receiving your messages. Suppression lists serve as a “do not contact” list for your email sends. Examples of the types of addresses included on a suppression list are addresses with a history of spam complaints, unsubscribe lists from previous providers or advertisers, addresses of your competitors, and canceled customers.
Thanks