The terms concave (has at least one surface that curves inward) and convex (has at least one surface that curves outward) are most commonly used to describe lenses and mirrors.  Concave lenses are used to correct nearsightedness, while lenses that are convex are used to correct farsightedness

Concave lenses are also used in binoculars, telescopes, and cameras to create the image.  Convex lenses are used in microscopes, magnifying glasses, and they are also used in cameras to focus light. 

2 hours ago, Bill W said:

The terms concave (has at least one surface that curves inward) and convex (has at least one surface that curves outward) are most commonly used to describe lenses and mirrors.  Concave lenses are used to correct nearsightedness, while lenses that are convex are used to correct farsightedness

Trivia! Thank you. I learned something new today. That makes it a good day. 😀