복잡하다 has two main meanings. 1. complicated, complex, intricate, tangled 일이 복잡하게 됐다 Things have become more complicated. 머릿속이 복잡하다 I have too many things to think about. 2. crowded (with), busy, congested 도로는 휴일 나들이 차량들로 복잡했다 The roads were crowded with holiday traffic. 아침에 지하철은 출근하는 사람들로 복잡하다 During the morning rush hour, the subway gets congested with commuters.

It can also be crowded ex) 명동의 거리는 항상 복잡하다.

It means "to be complicated".