noun
unofficial app; non-store app
Refers to a smartphone app distributed outside official app stores like Google Play or the Apple App Store, often via direct download or third-party platforms.
非公式アプリをインストールするときは、セキュリティに注意が必要です。
When installing an unofficial app, you need to be careful about security.
公式アプリ is an official app distributed through authorized stores, while 非公式アプリ is an unofficial app obtained outside those channels.
Compound of 非公式 (unofficial) and アプリ (app, from English 'application').