Crawled vs Managed Properties
SharePoint’s Content Processing Component parses properties and full text from the documents and data it’s sent from the Crawl Component.
Both the full text and the properties are sent to the Index Component for storing in the Index.
Each property is turned into a Crawled Property.
SharePoint Server Administrators can mark Crawled Properties for inclusion in the Full Text Index, which means they can be used in simple text queries when users perform a search.
By default, this is only enabled for Crawled Properties that are derived from SharePoint List or Library Columns.
If you want to enable a more specific search, that only brings back results where a specific property has a specific value, you must create a Managed Property and add a mapping between the two.
Managed Properties offer many more options for configuring the behaviour of Crawled Properties.