Packed with progressive elements, esp. regarding the genre adjective which applies to music - i.e. progressive rock, progressive metal, progressive folk, etc. "Progressive" generally connotes virtuosic instrumentation, incorporation of exotic sounds/instruments, use of uncommon time signatures, unusual/abstract lyrical subject matter, etc.
I'm sort of OK with Coheed and Cambria, I guess, but they are not nearly as proggy as Dream Theater or The Mars Volta. They sound like a less-proggy version of Rush, except Rush didn't have an emo influence.
Used to describe pyschadelic music with progressive tone changes, ie, progessive music. This music is so progressice that it is foggy and the notes kind of just float mid-air, barely changing at all. Also can be used when touting progressive music that you feel is exceptionally trippy. A stoner type term.
"that album is really proggy when you hear it on headphones"