Document libraries in SharePoint 2010 and 2013 include the ability to enable a special type of enterprise managed metadata Column called enterprise keywords. Unlike other managed metadata, enterprise keywords are stored in a single, flat list in a system term set called Keywords. In other words, there is no hierarchy of enterprise keywords. This Column can be added as part of a Content Type, or it can be enabled in a setting called Enterprise Metadata and Keywords Settings for a document library. If you enable enterprise keywords, users who have content contribution privileges can associate one or more keywords of their own choice to a document.
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