noun
downward compatibility; backward compatibility
Technical term for compatibility with older or lower-tier systems, versions, or components. Often used in IT and engineering contexts.
このソフトウェアは上位互換性があるので、古いファイルも開けます。
This software has backward compatibility, so it can open old files.
noun
upward compatibility; forward compatibility
Often considered an incorrect usage; the intended meaning is actually downward/backward compatibility. The term 上位互換性 literally suggests compatibility with higher-tier systems, but in practice it is frequently misused to mean the opposite. Learners should be aware of this common confusion.
See also: 下位互換性
「上位互換性」を前方互換性の意味で使うのは誤用とされることが多い。
Using 上位互換性 to mean forward compatibility is often considered a misuse.