The eyepiece is the small glass part you look through on a microscope, a telescope, or binoculars. One end of the tool points at the tiny thing or the far thing; the eyepiece is the end that meets your eye. You can often swap eyepieces to make the picture look larger or smaller. This is a science and hobby word. Though actually, the eyepiece is often more than one piece of glass hidden in a small tube — people still call the whole viewing end the eyepiece. Do not mix it up with the big lens at the other end, which looks at the object, not at you.