Around the age of 40, the lens of the eye becomes less flexible limiting its ability to focus for near tasks. This condition is known as presbyopia. Multifocal contact lenses provide correction for presbyopia.
A bifocal lens has two different powers in the lens; one for distance and one for close vision.
A multifocal lens has many different powers; distance, intermediate and near (with a whole lot in between). All bifocal soft lenses are in truth, multifocals. Gas-Permeable contact lenses can be either bifocal or multifocal.
Pros: A true bifocal lens will provide good distance and good near vision. A multifocal will provide good distance and intermediate. A multifocal will have no image "jump" between near and far and give you a truer vision, just like when we were younger.
Cons: A bifocal lens lacks intermediate vision (like at the computer). A multifocal lens can sometimes be not quite as clear up close (depending on your bifocal add).