seat; seat base
Refers to the part of a chair, bench, or similar furniture that a person sits on. Often used in furniture descriptions or repair contexts.
The seat of this chair has thick cushioning and is comfortable to sit on.
The seat of the old bench broke, so I replaced it with a new plank.
Compound of 座 (za, 'sitting') and 部 (bu, 'part'). The reading ざぶ is a straightforward on'yomi combination.