Masking is the process of revealing or hiding an object based on another shape. It establishes a relationship between an object and its utility.

Most designers are familiar with the masking tool. It's usually used for static objects like avatars, but this technique finds its application in motion too. Think of any music app — for example, Spotify. While the track is playing, its album cover and other details are hidden behind the mask so that you can browse the app. On click, the mask reveals the hidden content.