복잡해요 · 복잡했어요 · 복잡한 (+noun)
to be complicated; to be crowded, congested
Example
출근 시간에는 지하철이 너무 복잡해요.
The subway is really crowded during rush hour.
Word parts
복 double, multiple+잡 mixed
Literally 'many things mixed together'.
Good to know
Besides 'complicated', it's the everyday word for crowded places: 시장이 복잡해요.