Bifocal Lenses
Bifocal lenses have two powers - usually a distance portion that contains a lens with the distance prescription and a near area - that contains the prescription for close work.
The reading area can have different shapes - for example round or shaped like a D. The reading segment is visible on the lens.
Bifocal lenses have a segment for near work
The advantage of bifocals is that they give distance and near vision with no distortion. The disadvantages are that the segment is visible and hence is not cosmetically pleasing, the lens doesn’t give any intermediate vision - e.g. for the computer and as the eye moves into the reading area the image appears to jump.