Saved queries and filters are expressions kept in Coveo Enterprise Search's (CES) memory in order to be reapplied quickly. The difference between saved queries and filters is that saved queries do not accept additional expressions; whereas, saved filters do. For example, if the query Coveo AND Search is entered in the search box and the saved query @sysauthor=John is applied, Coveo AND Search is replaced by @sysauthor=John. However, if @sysauthor=John is a saved filter, it is added to the query expression to form Coveo AND Search @sysauthor=John.
Note: Saved queries and filters are optional, they can be removed in the Interface Editor (for more information, refer to Interface Editor Help > How to Modify Features).
See also: How to Add Saved Queries and Filters, How to Apply Saved Queries and Filters