Precalc
Working out the expensive stuff ahead of time — sine tables, distance maps — so the real-time loop only reads ready values.
Short for precalculation. Costly maths is done once before the run and stored in lookup tables: sine and cosine values, distance and angle maps for tunnels and plasmas, colour gradients. Per frame the effect just reads memory instead of computing.
On slow CPUs with no floating-point unit it is the difference between 50 frames a second and a slideshow. The cost moves to startup — the infamous precalc or loading bar — and to RAM, which in turn pushes the smallest productions toward sizecoding.