Half Bridge
The basic power stage block made of one high-side and one low-side switch, able to connect its common midpoint either to the supply or to the chassis line. On its own it drives one motor terminal; using two half bridges side by side forms an H-bridge.
The midpoint of a half bridge can be in three states: at the supply voltage while the upper switch conducts, at chassis while the lower switch conducts, and at high impedance while both are off. The fourth combination, both conducting together, is never permitted because it is shoot-through in the leg.
This block is the building stone of power electronics. Two of them drive a brushed DC motor in both directions, three of them drive a three-phase motor. The same structure is also the basis of buck-type switch mode power supplies.
Thinking in terms of blocks also makes fault diagnosis easier. If the motor runs in one direction and not at all in the other, the faulty part is most likely a single half bridge or the gate circuit driving it. By measuring both motor terminals with respect to chassis you can see which midpoint does not respond to the command. Before measuring, the supply must be disconnected and the mechanical load secured.
The context in which this term is used: DC Motor Driver Selection Guide