敲门

You use it as a verb-object phrase. You can say someone is 在敲门 (knocking on the door). You can also add a result, like 敲了三下门 (knocked three times). It’s a very active, physical phrase. Don't use it for digital 'knocking' like a ping unless you're being poetic.

Use it whenever you arrive at a friend's apartment. Use it at the office before entering a boss's room. It’s perfect for describing a scene in a story. If you hear a sound at night, you might ask, 'Who is 敲门?' It works in any physical setting involving a literal door.

Don't use it if you are ringing a doorbell. That is 按门铃. Also, don't use it for 'knocking' someone's confidence or 'knocking' a price down. It is strictly for physical doors. If you're 'knocking' on wood for luck, that's a different cultural concept entirely!

In China, knocking is a big deal for politeness. Traditional courtyards had heavy knockers, but today it’s mostly knuckles on wood. There is an old saying about 'knocking on the door' being the first step to opportunity. It’s seen as a sign of a 'well-bred' person to knock softly but clearly. Three knocks are standard; one is too aggressive, and a constant drumroll is just annoying.

You might hear 敲敲门 which makes it sound a bit more casual or tentative. There is also the 'knocker' itself, called 门敲 or 门环 in traditional settings. In a metaphorical sense, people talk about a 敲门砖 (a brick to knock on a door). This refers to a stepping stone or a credential used to open a career path.