A file caching mechanism used to increase performance
BLOB caching increases performance by caching frequently used files on the SharePoint server file system from the SharePoint content database. In addition, this feature enables byte-range requests for media files which is important for streaming media applications. This feature is used in conjunction with the Publishing feature and requires the Web Foundation service instance to be running. It is configured via a Web Application's web.config file in the element.
For more information, see TechNet: Plan for caching and performance in SharePoint Server 2013.