Scope Elevation Ceiling
The point at which a scope's internal elevation adjustment runs out and the shooter must hold over the reticle instead of dialing.
Every scope has a finite amount of internal travel, usually quoted in MOA or mil. Once you’ve dialed it all up, the only way to put the reticle higher than the target is to hold over: aim the bullet’s flight path with a marked stadia line instead of the crosshair.
The ceiling matters because rifles routinely outshoot the optics mounted on them. A .338 Lapua can carry to a mile, but a scope with only 25 mil of elevation on a flat base may not be able to follow it. Picatinny rails with built-in MOA (20, 30, 40) give back some of that travel.