What does it mean by lens element?

[Cane toad]

Im new and i see different lenses say 3 elements 2 groups or 5 elements 3 groups. What does this mean?

[David Metsky]

A lens element is a single piece of glass. They are many of them that make up a lens for various optics reasons. They are grouped together since they need to move when focusing or zooming.

-dave-