Energy weapons is an umbrella term for a variety of different weapon systems that are powered by technology that weaponizes both real-world and science-fiction physical laws (often a combination of both). Strictly speaking all weapons are energy weapons since some form of energy is needed to damage the target. Traditional ranged weapons use chemicals like gunpowder to deliver deforming kinetic energy to the target through bullets and grenades.
It is a common feature of many gaming energy weapons that these chemical explosives are not used. Often the emission of heat is used in a destructive manner instead of kinetic impact. Regardless of kind of technology the projectiles of energy weapons are depicted as pulses or beams of light. In real life these weapons are not realized in this way, because size, potential destructive force or power consumption would be unfavorable.
In video games energy weapons sometimes do not require ammunition, but require the player to manage heat generated by usage. In alien invasion scenarios the aliens often make extensive use of energy weapons, while humans stick to conventional projectile based armament. There are a few main groups of game energy weapons.
Macroscopic mass accelerators
This weapon type is more traditional in the sense that some kind of projectile is shoot at the enemy to deliver a damaging impact. Instead of using combustible propellant to accelerate the usually metal projectile they rely on electromagnetic fields. Weapons that work according to this principle are often called "Gauss guns", named after the German scientist, Carl Friedrich Gauss, who formulated the mathematical descriptions of magnetism. Other names include kinetic energy weapons, mass drivers or railguns. Examples include the Gauss-weapons in the BattleTech universe or the small arms in the Mass Effect games, the later also add the mass effect sci-fi concept to the mode of operation of such guns.
Particle Beam Weapons
Particle beam weapons shoot beams or bolts of charged or uncharged particles like electrons, ions or atoms at the target. Due to velocities near the speed of light the kinetic energy of those particles is high and is able to destroy the molecular structure of the target (surface). The serbian inventor and engineer Nikola Tesla envisioned the so called "death rays" at the beginning of the 20th century. His manuscripts vanished after his death leading to a lot of conspiracy theories. This weapon type includes the ion cannon, known for example as the ultimate weapon in GDI arsenal of the Command&Conquer games, and the ubiquitous plasma guns, which simply put fire super hot gases.
Electromagnetic radiation weapons
Most notably this category includes LASERS (Light Amplification by Stimulated Emission of Radiation). These heat up the target leading to violent evaporation of the target surface and shear between the affected and adjacent material. Laser weapons are featured in almost every science-fiction game.Somewhat similar are MASERS ("Microwave Amplification by Stimulated Emission of Radiation"), which emit EM radiation over a wide spectrum.
Less common are devices that weaponize sonic beams (Sonic tanks in Dune II) or electric currents (lightning bolts). These often work directly against human physiology, affecting gas nuclei in tissues or disturbing the electricity based nervous system respectively. Rarely, but prominently, some form of energy powers sword-like melee weapons such as the lightsaber or the Halo energy sword. These devices can not easily be connected to real world phenomena, without defying known physical laws.