Technical term used in engineering, architecture, and optics for an opening or orifice.
The aperture of this camera is very small.
Light comes in through the opening of the building.
read-write slot; read-write opening
Compound of 開 (kai, 'open'), 口 (kou, 'mouth'), and 部 (bu, 'part'). The exact historical derivation is uncertain, but the word follows standard Sino-Japanese word formation patterns.