Depenetration
The step that pushes two already-overlapping bodies apart along the shortest way out, before their velocities are resolved.
Collisions are rarely detected at the exact instant two surfaces touch; a body usually sinks some way into another during a frame. Depenetration moves it back along the contact normal by exactly the penetration depth, so the next step starts with the bodies separated.
The dose is a trade-off: push everything out at once and a stack of crates jitters nervously; push too little and heavy objects slowly sink through the floor. Most engines correct only a fraction per step and let the rest resolve over several frames — a deliberately sluggish but stable behaviour.