Every Android application runs in its own Linux process. Android starts the process when any of the application's code needs to be executed, and shuts down the process when it's no longer needed and system resources are required by other applications.

This is a core Android architecture principle. Each Android app runs in its own Linux process with its own Dalvik/ART instance. The Android system manages process lifecycle - starting processes when app components need to run and killing them when resources are needed elsewhere. This process isolation enhances security and stability.