Frame budget
How much time each frame is allowed to cost — 16.7 milliseconds at 60 fps — split up like a budget between the game's subsystems.
A game loop targeting 60 Hz gets 1000/60 ≈ 16.7 ms per iteration, 33.3 ms at 30 Hz and barely 8.3 ms at 120 Hz. In that window it has to read input, step logic and physics, blend animations and submit every draw call. Studios therefore allocate the time explicitly: so many milliseconds for AI, so many for physics, the rest for rendering — and whoever goes over gets to explain why.
Blow the budget and the frame misses its vsync and shows up one refresh late, which is the stutter that frame pacing exists to prevent. Dynamic resolution exists largely so the GPU's share of the budget can be adjusted on the fly. The demoscene's rastertime is the same idea, measured in scanlines instead of milliseconds.