Filters are used to narrow down the set of records to be retrieved when an audience instance is run.
A filter must always be associated with a single selection rule. The selection rule is applied to the output, or one of the outputs, of the block that precedes the filter (if one exists) in order to further refine the data set.
For example, consider an audience that contains a filter, to which a selection rule that selects only females is attached. Another filter is added, and a connection created from the original to the new filter. A selection rule that selects only married people is added to the second filter. The second filter is applied to the output of the first, so that only married females are selected.