Open entryway to a corridor, tunnel, conduit, Jeffries tube, branch of sewer, bag, etc.

Note from Okrand:

What I was driving at is that a qa'rI' at or from which one can enter or exit is a DIn. There may or may not be a (closed or open) door or gate there, but if there is, that door or gate is a lojmIt. That is, there's no special word just because it's a qa'rI' door.

(By the way, a doorframe or something similar – something constructed to hold a door or gate, whether the door/gate is there or not – is a lIvqa'nan.)