Progressives (or multifocals, no-line bifocals) are lenses with 3 zones of focus but no hard lines.
Althought you get the benefit of having no line in your lenses, Progressives will have areas of distortion on either side of the lens.
As we age, It becomes more difficult to look at objects that are close to our eyes. This is a
very common condition called Presbyopia. Most people first notice when they have trouble reading
fine print, or when they have headaches after reading, due to eyestrain.
Bifocals were invented to alleviate this condition by adding a reading power to the bottom half of the lens, so that people could see distance as normal, then look down for a reading power.
Progressives are intended for people who need correction for Presbyopia, but do not want a hard line in the middle of their lenses.