When you need to see something in more detail but are at the physical limits of ordinary human vision, you can use a convex lens mounted in a frame — a magnifying glass — to bend light such that smaller details are visible. This kind of thing is also necessary on computers, because displays have limited space and resolution, and sometimes it is desirable to have one pixel appear 10 pixels wide on screen. (Very frequently when you are drawing pixel art!)
Although the magnifying glass remains a common sight across digital interfaces, the actual word “magnify” has largely been replaced by “zoom,” a term from the camera world. A zoom lens uses multiple internal lenses to bend light in complex ways that produce far greater magnification, factors of 10 or 100. Zoom factor on digital interfaces besides cameras, however, is typically represented by a percentage.