Starfield
The demoscene's first practice effect — points flying outward from a centre to fake the illusion of space flight.
A starfield simulates travel through space: points move outward from the centre of the screen, faster and brighter the "closer" they are, slower and dimmer further out. The parallax — layers moving at different speeds — supplies the depth. The effect is cheap to compute, often just a handful of additions per point, so it became the first thing almost every scene coder learned.
Simple variants merely scrolled stars sideways; fancier ones projected real 3D coordinates onto the screen. The starfield turned up in countless cracktros and demos, and became a clichéd but well-loved opener. Along with the rotozoomer, it belonged to the beginners' course in real-time graphics.