noun
unofficial app; app installed without carrier approval
Dated term from the feature phone era, referring to apps installed without the carrier's permission, often via sideloading. Compare 野良アプリ, which is a more common modern term for unofficial apps.
See also: 野良アプリ
On old feature phones, installing unofficial apps could sometimes void the warranty.
勝手アプリはキャリアの審査を通っていないので、動作が不安定な場合もあった。
Since unofficial apps didn't pass carrier review, they could be unstable.