What is Sticky Bit?

If sticky bit is active, that file can be only deleted by root or owner.

to activate;
chmod +t file.txt
-rw-r--r-T
to unactivate;
chmod -t file.txt
-rw-r--r--

You may also want to read this entry;
http://ozsoyler.blogspot.com/2015/01/what-is-suid-and-guid.html