1. file system check. The Unix program that checks a file system for internal consistency and bad blocks etc. and can repair some faults. fsck is often used after a crash when the file system has been left in an inconsistent state, e.g. due to incomplete flushing of buffers. 2. Used on Usenet newsgroup alt.sysadmin.recovery as substitute for "fuck" and became more main-stream after the Communications Decency Act.