(c) sticky(8)STICKY DIRECTORIES
A directory whose ‘sticky bit’ is set becomes an appendâ€only directory,
or, more accurately, a directory in which the deletion of files is
restricted. A file in a sticky directory may only be removed or renamed
by a user if the user has write permission for the directory and the user
is the owner of the file, the owner of the directory, or the superâ€user.