Search filters or hedges are search strategies that include a series of pre-elaborated free text terms/text words/phrases and subject headings for a given concept, idea, or study design. Though the terms "search filters" and "hedges" may be used interchangeably, search filters refer to methods that refine static concepts, such as study design, whereas hedges deal with subject materials.
Useful sources of general search filters
Tools for developing a search strategy
Campbell, Sandy. Filter to Retrieve Studies Related to Animals from the OVID Medline Database. John W. Scott Health Sciences Library, University of Alberta. Rev. February 26, 2020.
https://docs.google.com/document/d/1mpqZsuCPCbCxmFUf5ndjIUaCCbyu-UmMyWlGGydVgwE/edit
Campbell, Sandy. Filter to Retrieve Studies Related to Watchful Waiting from the Ovid MEDLINE Database. John W. Scott Health Sciences Library, University of Alberta. Rev. November 26, 2015.
http://guides.library.ualberta.ca/ld.php?content_id=14026757