I had never heard of 'Airsoft' until about 20 minutes ago, but I'm going to try and explain it: it's like paintball, except there's no paint, and real actual ballistics are involved. Instead, non-metallic pellets are fired from replica guns. It sounds and looks like a lot of fun.
Particularly if you take the time to design and build incredibly intricate replicas of Halo weapons.
The weapon, in this case, is the Spartan Laser.
The details on this replica are absolutely ridiculous. It doesn't function like that actual Spartan Laser, which was sort of like a future laser thing that completely destroyed vehicles on one shot. This is more like a pulse rifle of sorts, but it does seem to 'charge' in its own weird way.
Regardless, this thing is bloody beautiful, and almost single-handedly explains to me how people can become obsessed with firearms.