Raycasting
A rendering technique that shoots one ray per screen column into a 2D grid map to draw walls, faking 3D cheaply.
Raycasting, popularized by id Software's Wolfenstein 3D (1992), renders a pseudo-3D view from a 2D map. For each vertical column of the screen it casts a ray across the grid until it hits a wall, measures the distance, and draws a vertical slice whose height is inversely proportional to that distance. No polygons, no heavy floating-point math — it ran on a 386.
Because the walls are grid-aligned and all vertical, there are limits: no sloped floors, no looking up or down, no overlapping rooms. Doom (1993) replaced the grid with a BSP-partitioned level to allow non-orthogonal walls. Raycasting is not the same as ray tracing, which traces many rays per pixel for physically accurate light; raycasting traces one ray per column for speed. Voxel-terrain engines like Comanche used a related per-column height trick.