Camera dead zone
A region of the screen inside which the player can move freely without the camera following; only when the character reaches its edge does the view start to scroll.
A camera locked dead centre on the character drags the whole world along with every small step and every jump, which tires the eyes and makes the level hard to read. The dead zone, also called a camera window, lets small movements stay inside the frame. In platformers it is often taller than it is wide, so jumps don't yank the camera up and down, and vertical tracking waits until the character lands on a new level.
Super Mario Bros. in 1985 scrolled only to the right, and only once Mario passed the middle of the screen. Later games added lookahead in the direction of travel and smooth easing with spring-damper motion. Itay Keren catalogued the variations in his GDC 2015 talk "Scroll Back", which has since become the standard reference.