The Lead is the leg of the dog that is in front while in any given gate. If it is the right paw that stretches out first and furthest, then the dog is on a Right or Clockwise Lead. If the left paw goes first and furthest, then it is a Left or Counter Lead.
The dog’s lead changes with the Flank (the leg on the inside of the turn leads) and with the stance and pressure of the handler. Change the stance from clock to counter and you change the lead as well.