1) Lens type 
Having three foci. ... See: trifocal lens. ... (05 Mar 2000) ... 
(TRI-foh-kul) Eyeglass lens that incorporates three lenses of different powers The main portion is usually focused for distance (20 ft), the center segment for about 2 ft, and the lower segment for near (14 in)
Type: Term Pronunciation: trī′fō-kăl Definitions: 1. Having three foci. See: trifocal lens
trifocal 1. Having three focal lengths. 2. Having one section that corrects for distant vision, a second section that corrects for medium vision, and a third that corrects for near vision, as an eyeglass lens.