An L-drive is a type of azimuth thruster where the electric motor is mounted vertically, removing the second bevel gear from the drivetrain.
Azimuth thruster pods can be rotated through a full 360 degrees, allowing for rapid changes in thrust direction and eliminating the need for a conventional rudder.
This form of power transmission is called a L-drive because the rotary motion has to make one right angle turn, thus looking a bit like the letter "L".
This name is used to make clear the arrangement of drive is different from Z-drive.