Zzap weapons are a special type of weapon exclusive to the technical knowledge of the Orks. They are roughly analogous to Ork laser weapons, however describing them as lasers is a bit of a stretch. In a weird way, they share more in common to the Imperium's lightning gun (a special type of las weaponry that causes electrical aftershocks) than tried and true laser. However, it could be deemed that the Zzap weapons uses some kind electromagnetic beams to mimic a laser.
The elusive nature of Zzap weaponry had once caught the interests of the Imperium. Interested as to how the Orks were able to acquire such technology, the Imperium once monitored a Mekboy constructing a Zzap gun. Yet when he was interrogated, the Imperials found that the knowledge for creating it was innate to the Ork race. These weapons are currently considered (probably out of jealousy) Xeno-heresy by the Adeptus Mechanicus. Standing orders to Imperial troops are to destroy them when encountered.
The most common type of Zzap weapons and one that is part of the Mek Gunz selection of heavy support. A Zzap Gun consists of a wire-bound tube and a powerful generator at the back end of it with a lot of custom 'gubbinz'. Although potent, its power is determined by the willpower of the grot firing the weapon, as its firing lever also electrocutes the Gretchin firing it.
It represents the pinnacle of Ork technological advancement. An extremely powerful weapon, the Zzap gun serves a role not dissimilar to an Imperial Lascannon in that it fires concentrated beams of energy effective against vehicles. Although powerful, this weapon suffers from the common maladies of all Ork weapons and as such can vary to have such devastating power that it is stronger than anything in the Imperium, but some unlucky shots won't be strong enough to even scratch enemy armour. It is usually mounted on Ork Vehicles but sometimes is manned by Grots as a Big Gun.
The Zzap Gun on steroids.
The Big Zzappa is a heavier and more potent version of the Zzap Gun that shares its advantages, has longer range and is even more unpredictable when fired. It is mounted on heavier Ork vehicles such as Gunwagons, Big Trakks or Battle Fortresses.
Sometimes however, a Big Zzappa can act as a stationary turret, blasting apart encroaching enemy armor in a few shots and turning infantry into a seared shadow. On the other hand, like the smaller Zzap Gun, the usefulness of the Big Zzappa is all based on a gamble and has a probable chance on barely tickling a sunburned Imperial Guardsmen on Mordia.
Gaze of Mork
A giant Zzap weapon found only on the Ork's biggest machines.
Stompas are often seen as gigantic representations of Ork Gods like all other Gargants and it is quite common for them to have life-like heads. Gaze of Mork (or, possibly, Gork) is an enormous and unpredictable force beam generator, built in into the head of the Stompa. It varies in design but is usually mounted to fire from Stompa's eyes. In characteristics it is similar to Zzap Gun, but much more powerful then even a Big Zzappa.
They are just as unpredictable, with the beam that can melt a Baneblade with its first shot, and fail to kill a Guardsman with the next- or do anything in between. Meks often delight in diverting the power of the Stompas roaring engines, giving them enormous power. Such devastating power can tear even the mighty Titans of the Adeptus Mechanicus asunder in a storm of energy so all Orks' enemies are right to fear the mighty gaze of their gods.
Soopa Zzap Gun
The biggest Zzap weapon to date and one that can pose a threat to superheavies.
The Soopa Zzap-Gun is a monstrously huge and powerful version of Zzap Gun that can be mounted on Ork Gargants, Gunwagons, Gunfortresses or used as a static anti-Titan gun. This thing is the more beamy version of the regular Soopagun, another oversized artillery piece that can shatter superheavy tanks in one shot. It could be said that the Soopa Zzap Gun has the power to rival that of the main armament of a Shadowsword, which is the Volcano Cannon.
Therefore, Titans are vulnerable to these weapons and the Soopa Zzap Gun can be strategically placed on its own, acting as a giant sniper rifle to snuff out God Machines.