BCA - UNIX and Shell Programming

The sticky bit in the mode of a Unix file tells the kernel to retain the code loaded in swap space long after it has finished executing on the presumption that it will be used again shortly if it is set for an executable.
To avoid reloading commonly used applications like the shell or vi from disc, this performance enhancement was implemented in several early (and recent?) Unix versions.

If the sticky bit is set on a directory, an unprivileged user may not delete or rename files of other users in that directory even if he has write access to the directory.

The Unix "ls" command displays a set sticky bit as a "t" in the permissions of a file or directory.