It depends on what race you are running. For example In the 4x100 the 3rd leg is your closer he/she is the person who makes up for the lost time if the 2nd leg isn't fast enough and your 4th/ last leg take it home he's/she's your fastest.
It means you are the third person to run in the race
US lead off runner Manteo Mitchell in the 4x400 relay (he had broken his left fibula)
3, Original to second leg, second to third, and third to final runner.
2nd
It simply means you are the first person on your relay team to run :D
Yes, you have because you have to run a complete lap around the stadium
typically a relay has four "legs" or four different runners. Each must finish a specific distance (often one lap around course) before next runner can start. The first runner is the "first leg" of the relay.
anchor
Each segment of the relay is referred to as a leg.
last man
8.8 secs
Leg
at competitive galas, usually 4. occasionally 8. :)