A laser diode (LD, also injection laser diode or ILD or semiconductor laser or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction.

A solid-state laser is a laser that uses a gain medium that is a solid, usually a crystal or glass. Semiconductor-based lasers such as laser diodes are generally excluded; treated as a separate class of laser on their own.