This is the 2129th most frequent Chinese word.
孔
"孔" means "hole" or "opening."
In this sentence, "孔" refers to a small opening or hole.
壁上有一个小孔，可以通风。
There is a small hole in the wall to allow ventilation.
Here, "孔" is part of the term "针孔" (pinhole), denoting the small aperture in a camera.
针孔摄像机能够偷偷记录画面。
The pinhole camera can secretly record pictures.
In this example, "孔" represents an opening through which the line is threaded.