spare parts; reserve supplies
Refers to items kept in reserve for replacement or emergency use, such as spare parts for machinery or backup supplies.
Keep spare parts on hand in case of breakdowns.
This factory always maintains a stock of reserve supplies.
スペアパーツ is a loanword from English 'spare parts' and is often used in technical or mechanical contexts, whereas 予備品 can also cover non-mechanical reserve supplies.
Compound of 予備 (yobi, 'reserve, spare') and 品 (hin, 'article, goods'). The term straightforwardly means 'reserve goods'.