noun which may take the genitive case particle 'no', noun
extremely crowded; packed
Colloquial noun/adjectival noun used to describe places or situations that are extremely crowded, often with a sense of frustration or exaggeration. Commonly used in casual speech and online posts.
週末の遊園地は激混みだった。
The amusement park was extremely crowded on the weekend.
この時間の電車はいつも激混みだ。
The train at this hour is always packed.
Compound of 激 (げき, 'intense') and 混み (こみ, noun form of 混む 'to be crowded'). A relatively modern colloquial formation.