Match Any or All Criteria?

Determines whether the selection criteria are combined with an AND or with an OR. If 'AND' is selected, then the resulting subset will be the intersection of the sets defined by each criterion. If 'OR' is selected, then the resulting subset will be the union of the sets defined by each criterion.

For example, let's say you have two additional columns in your members table: one column specifies the kind of pet a member has (the pets column), and the other column specifies the country a member lives in (the country column). If you'd like to create a subset which would send to all the cat owners in England, you'd use AND. If you'd like to send to all cat owners anywhere in the world and to everyone on your list who lives England, you'd use OR.