File Cache is a Symantec Endpoint Protection (SEP) feature enabled by default.
Auto-Protect uses a file cache so that it remembers clean files that have already been scanned, in order to speed up repeat-access to commonly used files. The file cache persists across startups.
With the "Rescan the cache when new definitions load" option checked, files in the recently-scanned cache will be rescanned in the background after a definition update, to ensure that they are still considered clean by the updated definitions, and to avoid delays from having to scan the files the next time they are actually accessed by an application.
With the "Rescan the cache when new definitions load" option unchecked, the cache will be cleared when definitions are updated or the computer is restarted. No background-scan of the files listed in the cache will be launched. The next time files are accessed and scanned they will again become listed in the cache.
The setting can be found under Auto-Protect Advanced Options.