What separates proscenium theater from popular theater?

Proscenium Theatre refers to the structure itself and Popular Theatre refers to modern Theater as an art . Unless you are refering to a specific theate period like the chief form of drama in Ireland from 1820-1899. If that's confusing than how about this: a proscenium theater is referring to the shape of the stage itself, a stage that has a proscenium arch as apposed to a thrust stage theater which has a stage that comes into the audience.