Suppressions blocks are similar in nature to filters; however, they differ in two fundamental respects.
Firstly, a suppressions block is not used to target records - rather, it defines the records to which messages should definitely not be sent. These may include records of the deceased, and those who have explicitly requested not to receive communications.
Secondly, a suppressions block may contain more than one selection rule, in contrast to a filter's single rule. A suppressions block ensures that all records identified by its selection rules will not be targeted when an audience instance based upon its parent template is run.
Note that a suppressions block must contain at least one suppression.