Generally it refers to too many people in a small space.
Crowded
The comparative form of "crowded" is "more crowded."
Yes. "Crowded" can be a verb (as in "People crowded the stadium") or an adjective. (as in "The stadium was crowded because of all the people.")
Yes. Very crowded.
Its VERY crowded
The room is crowded.
Diffusion
That is the correct spelling of crowded (congested, cramped).
Is coach too crowded
Crowded House was created in 1985.
Crowded House ended in 1996.
Crowded Paradise was created in 1956.