a lens, esp. for eyeglasses, with one part ground for close focus, as for reading, and the other ground for distance
See bifocal in American Heritage Dictionary 4
adjective
Having two focal lengths.
Having one section that corrects for distant vision and another that corrects for near vision, as an eyeglass lens.
Embodying two distinct and often conflicting goals, interests, or courses of action: “a smoothly functioning bifocal mind”(John McPhee).“A bifocal monetary policy . . . has kept one eye on the money supply and the other on interest rates”(Edward Meadows).