The phrase refers to obtaining Android application package files from unofficial sources. These sources operate outside of the established app distribution channels like Google Play Store. A user might, for example, seek an older version of an application or a modified app lacking certain restrictions through these alternative avenues.
The allure of these sources often stems from the availability of apps not found on official platforms, or from the promise of free access to paid applications. Historically, individuals seeking greater control over their devices or access to region-locked content have turned to these methods. However, downloading software from unverified vendors introduces security risks and potential legal ramifications.