Bullet hell
Also said as Shmup, Shoot 'em up, Danmaku, Curtain fire
A shooter whose screen fills with slow, patterned enemy fire that you thread through. It promises calm inside chaos. Your real hitbox is far smaller than your ship, which makes it possible.
The patterns look impossible and are not. The gap between how close you seem to come and how safe you are is what makes the player feel superhuman.
Say it
“Make the hitbox a 4-pixel dot at the ship's centre, drawn only while focused, and score each bullet that passes within 24 pixels as a graze.”
Where you’ve seen it
Cave's DoDonPachi (1997) helped set the style. Touhou Project games show your tiny real hitbox as a dot when you slow down, and they count and score each graze, so a close pass earns something instead of only being survived.
Not to be confused with bullet heaven
In a bullet hell, the screen full of bullets is aimed at you. In a bullet heaven, the screen full of bullets is yours.