An additional rail usually found in subway systems, running parallel to the existing tracks, and sometimes slightly elevated. The third rail carries a live electric current which is used to power the subway trains.
The term THIRD RAIL commonly is a low pro way of refferancing one's Cock, mostly used when talking directly to or within ear shot of some bitches. Can be used to insult, make fun of with out them really catching on, or as a little bit of "verbal bling" while telling a story.
"sup, you ladies down with the trird rail or what?"