Android apps are programs in software that can be installed on devices that run the Android operating system. These apps are either pre-installed with the OS, or can be downloaded and installed at a later time.

Android app development is based on the use of the Java programming language, which permits rapid development of apps. The modular design of the language encourages reuse of code and includes the most productive tools, such as emulators, IDEs (integrated development environments) and built-in platform support such as Google Cloud Platform.

With Android, developers can also benefit from the many APIs and tools to create complex and robust apps. This includes the Google Play Services, which includes a wide range of functions like maps, search, and social integrations. Google also encourages transparency within its OS by permitting independent evaluation of its source code, which helps ensure the stability of the platform as well as increasing the trust of developers.

Android also offers advanced security features to protect apps against attacks and data breaches. These include app signing, which restricts access to the file system only to the developer, and security libraries that allow biometrics, user authentication and encryption.

Android is the most well-known mobile OS with an extensive range of users. App developers looking to offer a consistent experience can face challenges because of the diverse ecosystem of Android devices. Developers who are proactive face this challenge with responsive design and compatibility tests to ensure seamless user experience across all devices.