extension; extended part
Computing term for an add-on, plug-in, or a part that extends functionality of software or hardware.
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ソフトウェアの拡張部分は別途ダウンロードが必要です。
The software extension needs to be downloaded separately.
拡張 is the general noun for 'expansion' or 'extension', while 拡張部分 specifically refers to the extended part or module.
アドオン is a common loanword for software add-ons, often used interchangeably with 拡張部分 in computing contexts.
Compound of 拡張 (expansion) + 部分 (part). The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning.