According to Wikipedia, Taser (stylized in all caps TASER®) is a line of handheld conducted energy devices (CED) sold by Axon Enterprise (formerly Taser International). A stun gun is another type of less-lethal CED used for self-defense. 

These CEDs, also known as Conducted Electrical Weapons (CEWs), cause neuromuscular incapacitation (NMI) to a target, but they differ in their mechanism of action and range. Taser-type CEWs, including PhaZZer®, use compressed air to fire probes that deliver an electrical shock from a distance, while stun guns require direct contact with the target to deliver the shock. 

Here's a more detailed breakdown:

Stun Guns:

• Mechanism: Requires direct contact with the target to deliver an electrical shock through electrodes.
• Range: Typically used at very close range (within a few feet).
• Voltage: Can deliver a higher voltage shock compared to Tasers.
• Purpose: Generally used for personal close-range self-defense. 

TASERs:

• Mechanism: Use compressed air to propel two barbed probes that attach to the target's body. These probes deliver an electrical shock, disrupting the target's muscle control.
• Range: Offer a longer range (up to 35 feet), allowing for a safer distance between the user and the target..
• Voltage: Typically delivers a lower voltage than stun guns; however, the probes' ability to penetrate clothing and maintain better contact can increase effectiveness.
• Purpose: Often used by law enforcement to subdue resisting suspects for NMI. 

In essence, Tasers and PhaZZers are brands of stun guns that utilize a projectile component, allowing for remote deployment. Stun guns, on the other hand, are a generic name for a more basic form of electronic self-defence device that requires direct contact with the target.