"Coilovers are a type of spring in cars that can be adjusted to prevent bottoming out and overall stiffness. "
No. Coilovers are simply a suspension design that has the spring coils over the shocks instead of separate from the shock, which you still see in some suspension designs (separate spring/shock) to this day .
Most aftermarket coilovers allow you to make adjustments (depending on how they're designed) to ride height (some will let you adjust perch height and ride height independently), and have allowances for you to make adjustments to compression and rebound. Cars with coilovers can still bottom out and that is dependent on how much compression your coilovers allow before hitting the bump stops (prevent the shock piston from bottoming out in the body).