When you create an ad-hoc query, you can use an existing selection of records that match the query's source view record type to create output fields and filters. A selection is a named set of IDs of the same record type. For information about selections, refer to Selections.
If you use a selection as a filter in a query, you specify whether the records to include in the results exist in the selection. This saves you time because you do not need to recreate the selection's filter criteria.