bunched up; crowded together; clumped
Describes people or things packed tightly together like dumplings on a skewer. Often used for crowded trains, clumped objects, or tangled hair.
The morning train is always packed like sardines.
My hair is all tangled up and the brush won't go through.
満員 simply means 'full' or 'crowded', while 団子状態 emphasizes being squashed together in a clump.
ぎゅうぎゅう is an onomatopoeic adverb for being tightly packed, often used with 詰め. 団子状態 is a noun describing the resulting state.
Compound of 団子 (dango, 'dumpling') + 状態 (jōtai, 'state'), from the image of dumplings stuck together on a skewer.