the opening into a structure: the doorway or entrance of a tent, house, gate, or city, the place where you go in or come out.
This word names the gap that lets you pass in or out: the doorway of a tent, the entrance of a house, the opening of a gate, the mouth of a cave, the way into a city. It is the space itself, not the door panel that swings shut over it (that is a separate word) and not the act of opening (which is a related verb). Because it is the threshold, it is the spot where two worlds meet, inside and outside, so a great deal of biblical life happens right there: visitors are greeted, judges and elders sit, business is settled, and people watch and wait.
It is the regular word for the entrance of the tent of meeting, the doorway where Israel brought its offerings and met with God. That single phrase, the doorway of the tent of meeting, runs through Exodus, Leviticus, and Numbers more than any other use of the word, fixing it as the appointed place where a worshiper stepped from common ground onto holy ground.
The same plain word stretches easily into pictures without changing its meaning. Sin crouches at the doorway, ready to spring. Wisdom calls out at the city entrances where the crowds pass. A wise person guards the opening of the mouth, the way words come out. In every case it is still simply the opening, the place of passage, used to make a vivid point.