Indirect drive means that the item creating motion is not fused or coupled in-line to the item that it is driving. For example, most servos have potentiometers inside for use of feedback. The potentiometer is typically directly below the splined output shaft of the servo and the shaft profile of the potentiometer matches the bore in the back of the final gear of the servo. This would be considered direct-drive. If, however the final gear of the servo had a gear on the bottom which mated to a gear on a potentiometer (no matter the ratio created by these two gears) the setup would be considered indirect drive.