Manage the search schema in SharePoint Server 2013

Crawled properties are metadata that is extracted from documents during crawls. Metadata can be structured content (such as the title or the author from a Word document), or unstructured content (such as a detected language or extracted keywords).

Users can only search on managed properties and not on crawled properties. To make a crawled property available for search queries, you must map the crawled property to a managed property. You can map multiple crawled properties to a single managed property or map a single crawled property to multiple managed properties

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