A physical or geographic point that controls passage, or a place that functions as an entrance or gateway to somewhere.
I showed my passport at the border checkpoint.
その港は大陸への関門として栄えた。
The port prospered as a gateway to the continent.
Figurative use for a difficult stage that must be passed before reaching a goal, often with exams, selection processes, negotiations, or projects.
一次試験が最初の関門だ。
The first exam is the first hurdle.
資金集めが事業を始める上で大きな関門になる。
Raising funds will be a major obstacle in starting the business.
You need a permit to pass through the checkpoint at the border.
He got through the hurdle of the final interview.
I have to overcome the hurdle of the qualifying exam.
The document screening is the first hurdle in getting hired.
The ship passed through the harbor's gateway and out into the open sea.