Bifocals are glasses that have two different strengths of lenses depending on where you look through the lens. Typically bifocals for presbyopia and myopia have the lower section (for use during reading) 1-2 diopters weaker than the upper section. The EM method uses separate differentials and normalized lenses rather than bifocals, making it easier to adjust your lens selections separately.
Bifocals are a type of multifocal, any lens with more than one power is a multifocals. Multifocals have a wider variety of available patterns than typical bifocals, such as gradual transitions and alternate patterns of power distribution.
Simultaneous vision lenses
A multifocal solution generally used in contacts, where your eye is looking through both powers of lens at the same time, and your visual cortex works out which part of the image to process for each distance.