Definition from Wiktionary, the free dictionary
From bi- + focal (see focus), coined in 1824 by John Isaac Hawkins, inventor of trifocals. When the concept of bifocals was originally conceived by Benjamin Franklin, he called them double spectacles.
bifocals (plural only)
- spectacles that have corrective lenses of two different powers; used by people who need both distance and reading glasses
spectacles with two different powers