This is the 3485th most frequent Korean word.
막힌
"Blocked" or "clogged."
Here, '막힌' describes the condition of the traffic being blocked or congested.
교통이 막혀서 늦었어요.
I was late because the traffic was congested.
In this context, '막힌' metaphorically refers to the way of thinking being blocked or not open to new ideas.
너무 막힌 사고 방식이에요.
That's a very closed-minded way of thinking.
Here, '막힌' literally describes the drain being physically obstructed.