Wasn't Yes like that. I've listened to a few of their songs and just don't get it.Prog Rock, short for Progressive Rock, is a subgenre of Rock music where the songs are generally longer than "pop" rock songs and tend to "progress" through a number of different musical ideas rather than sticking with one feel/idea/theme throughout the song.
Often the music will contain clever music theory ideas in the compositions, such as unusual time signatures (for example, instead of the beat count for a single phrase being "1,2,3,4,repeat" it might be "1,2,3,4,5,1,2,3,4,5,1,2,3,4,5,6,1,2,3,4,5,6,7,8,9,repeat").
Bohemian Rhapsody is an example of a progressive rock song.