In computer graphics, clipping is the intersection of two objects such that one obscures the geometry of the other, concealing it from view. In video games, clipping is related to "collision detection," the collection of algorithms that react to the interaction of two adjacent or overlapping geometries.
For example, when a video game player moves their character into a wall, the character's position stops, because it "collided" with the wall. The collision is determined on the character's "bounding box," a simpler, invisible geometry that roughly defines the volume of the character for the purpose of collision detection. Because the bounding box is not the same as the geometry of the character's model, parts of the visible geometry may "clip" through the wall surface. The character's hand may disappear into the surface of the wall, for example.
In speedrunning, noclip or noclipping is a common technique for bypassing game content. For example, if a character can be positioned such that proper collision detection is circumvented, the player could pass through a door without having the key. "Clipping" through the door (bypassing the designed collision detection) would enable the player to skip a required task, speeding up completion of the game.