backward compatibility; downward compatibility
Technical term used in computing and engineering to describe a system's ability to work with older versions or legacy components.
This software has backward compatibility, so it can open old files as well.
新しいハードウェアは後方互換性を確保する必要がある。
New hardware must ensure backward compatibility.
上位互換性 means 'upward compatibility' (compatibility with newer or higher-spec systems), while 後方互換性 refers to compatibility with older or lower-spec systems.
前方互換性 means 'forward compatibility' (designing a system to work with future versions), whereas 後方互換性 focuses on compatibility with past versions.
Compound of 後方 (kōhō, 'backward') + 互換性 (gokansei, 'compatibility'). The term is a calque from English 'backward compatibility'.