If you want to be pedantic, every weapon is an energy weapon. The only difference is the method by which energy is transferred from the gun to the target.
Now, when most people refer to energy weapons, they refer to lasers. Lasers are essentially flashlights that put out large, short bursts of energy at either visible or invisible wavelengths.
Paula Tormeson IV said:
I would think that "plasma weapon" is a sub-category of "energy weapon". Certainly there can be types of energy weapons that cause a bullet-like impact when shot at a target. From Wiki:
Pulsed Energy Projectile or PEP is a technology of non-lethal weaponry currently under development by the U.S. military. It involves the emission of an invisible laser pulse which, upon contact with the target, ablates the surface and creates a small amount of exploding plasma. This produces a pressure wave that stuns the target and knocks them off their feet...
The distinguishing between what you might call a plasma and an energy weapon is a bit hard to understand. A 'plasma weapon' would be considered something thats shoots plasma towards the target. This PEP weapon is a laser that makes a lot of short laser pulses which ionizes the subject matter, creating plasma. Since the weapon is shooting a laser, it is a laser weapon.