Energy weapons do energy damage (with the exception of the Graviton Beam). They generally have good accuracy but short range and poor flux efficiency. Energy weapons have unlimited ammo (except for the Antimatter Blaster), but some energy weapons such as the Burst PD Laser and Autopulse Laser have a limited number of charges which are restored over time; the number of charges can be increased with the Expanded Magazines hullmod.
A notable subset of energy weapons are the beam weapons. Beam weapons are perfectly accurate, and tend to have longer ranges and be more flux-efficient than pulse weapons. However, they have lower DPS and can only deal soft flux damage to shields.