TESLA is a glitch that allows motors to power a vehicle from an infinite distance away.
The glitch is caused by separating a contraption (for example, a block containing motors and a small car) through the use of TNT without breaking any parts. The easiest way to do this was to connect the two parts with two springs with one piece of TNT in the middle.
If done correctly, the physics engine would detect the car being separate from the motors, although the game engine would not detect the separation since no parts were broken (and no decouplers were used) and would still think the motors were connected to the vehicle. This allows small vehicles to travel at extremely fast speeds. Furthermore, the glitch can be used in Road Hogs levels to achieve 0-second records if the pig is part of the "motor box", since the timer only starts when the pig moves.
The glitch was patched in the Cake Race update. Springs are now less durable and will frequently break if TNT is detonated next to them, and Superglue can not fix this. However, TESLA was made obsolete before that point (in the Custom Contraptions update), when a new variation of the Electric Motor that could propel vehicles to speeds that were previously only achievable through TESLA was introduced. However, 0-second records are no longer possible in Road Hogs levels.