In Warhammer 40,000, "shooty" is
player slang a highly technical term used to describe a unit or army that is designed around ranged engagement rather than close combat. Tau armies in particular are typically shooty armies, since they have very powerful ranged weaponry but are poor at mêlée. The Imperial Guard are also sometimes considered a shooty faction, because their flashlights do (slightly) more damage than their shitty melee. The Orks are also very "shooty" as they just don't care what the hell they're killing with, just so long as they're killing, but they will almost never hit anything if they are more than a few inches away from their target. The green bastards can even shoot heavy weaponry while moving, which is pretty badass.
Necrons are also shooty, though in prior editions they could fight pretty damned well in melee combat in a pinch, especially with disruptor fields because then they would get gauss rules at any range. These days the 'Cronz can field several capable counter-assault units like Flayed Ones and Lychguard to defend their primarily shooty gunline.
Certain Space Marine and Chaos Space Marine chapters and legions, like the Salamanders and Iron Warriors, were also shooty-oriented; though the 4th edition Chaos Space Marines codex eliminated any mechanical differences between the Traitor Legions, you can still build a shooty oriented Chaos Space Marines army.
You can build a shooty Tyranid army by choosing an army primarily consisting of Termagaunts, Biovores, Gargoyles, Tyrannofexes, Tervigons, Venomthropes, Zoanthropes and getting ranged biomorphs for Warriors, Raveners, Shrikes, Carnifexes, Hive Tyrants and getting the doom of Malan'tai - you'll probably lose a hell of a lot though.
Eldar armies can also be built to be shooty, but it's generally not recommended if the enemy has anything capable of closing the distance and assaulting at all. That was until 6th edition, when Eldar got access to a bunch of fun shootyness that basically tore the MEQ metagame in half.
The opposition of shooty is, of course, choppy.