It is the transition area between new worlds.
I think Knock on the door makes more sense. Knock at the door.... What do you knock on at the door? the wall?
Door jamb is the name for the frame of a door. That is the normal proper use. Door jam COULD be used if the door is stuck and will not open, but would not be the ordinary use.
Who is knocking at the door
a door
Door is a noun not a preposition.
oiling a squeaky door
Brush
The Franks went into the company building where Otta franks worked. They had a annex which was located above the building. They had a secret door and they placed a book shelf in front of the door.
To stop your kitchen and dish washer door from squeaking try oiling or greasing the hinges.
what is the significance of having a bird nest on the front door
The Morning the Franks left, they left there door open and their room a mess so it looked like they had been captured by the Nazis. They actually were hiding in Amsterdam in a secret room. The door to the room was a bookshelf and they had to be quiet during the day. The door was dead bolted, but someone found out they were there, they told the Nazis, and The Franks were caught.
It should close tightly unless it's broken. So, I'd suggest fixing and/or oiling it. Last resort: just slam it.
Try oiling the hinges on the door. Replace the check strap. That is the part between the two hinges.
They put a wooden bookcase over the door. It still opened and shut, just hidden.
A good oiling of the door latching device with a thin oil works in most cases. Replace the door ajar switch that plugs into the door latch from inside the door. These switches are notorious for going bad...causing the dome lights to come on randomly, even when parked with key out of ignition, causing dead batteries, etc. Moderate difficulty to change switch. Part costs about $20. Not a job for rookies.
I would suggest to you that this means nothing of any significance. It is not superstitious. To believe that it signifies something is superstitious however.
It's a method of soliciting sex from strangers. Means the door's unlocked and you're ready for shoeless fornication in bare naked feet.