Hitbox

A hitbox is an invisible shape commonly used in video games for real-time collision detection. It is often a rectangle (in 2D games) or cuboid (in 3D) that is attached to and follows a point on a visible object (such as a model or a sprite). These are used to detect if you got hit by a enemy/fall damage.

Super Mario 64's Hitboxes are mostly cylinder, secrets might act as if they were hit, take for example SSL (Shifting Sand Lands), by touching the top of the hitbox, it registers as a +1, even tho the coin (aka secret) was never collected.

Pannenkoek2012 goes in depth of the Secret and Coin Hitboxes: Video