The joint on the inner end of the tie rod which attaches the tie rod to the rack and pinion. Usually a ball and socket joint.

The usual maintainance procedure for a tie rod end involves using a grease gun to pack grease into it(the tie rod end) through a special fitting called a grease zurt - which is, in fact, what most mechanic-type establishments refer to as a chassis lube. It's also customary to inspect the seals when performing this procedure.