Eyeglass lenses

Monofocal lenses are single-strength lenses and therefore correct either near or far vision (not intermediate distances). They are used to correct nearsightedness or farsightedness.

Multifocal lenses: what exactly do they mean, and what is the difference between bifocal, varifocal, and single vision lenses?

Multifocal lenses are ground to multiple strengths, allowing you to use them as both reading glasses and regular glasses.