The Locock Gambit is a very aggressive line in the Philidor Defense and starts with the moves:
The Philidor Defense is generally pretty passive. When you start out with e5 and d6 you are playing for a very long game by building up a strong pawn structure. This can be very frustrating for many players starting out with e4 because they are looking for an aggressive start.
With the Locock Gambit, white is able to regain the initiative and play a very aggressive line. The knight is sacrificed and in exchange, white is able to launch a strong attack against black
If you would like to learn more about each of these variations be sure to watch the video below.