noun
Technical term used in engineering, architecture, and optics for an opening or orifice.
このカメラの開口部は非常に小さい。
The aperture of this camera is very small.
建物の開口部から光が差し込む。
Light comes in through the opening of the building.
隙間 refers to a gap or crevice, often unintended, whereas 開口部 is a designed 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.