Sticky bit was used to trigger process to "stick" in memory 
after it is finished, now this usage is obsolete. Currently 
its use is system dependant and it is mostly used to 
suppress deletion of the files that belong to other users 
in the folder where you have "write" access to. 

Ex:
If set, then replaces "x" in the others permissions to "t", 
if others have execute permissions, or to "T" otherwise. 
Examples:
-rwxrwxrwt both others execute and sticky bit are set
-rwxrwxr-T sticky bit is set, but others execute is not set