Creating a Service
As noted previously, Android services are for long-running processes that may need to keep running even when decoupled from any activity. Examples include playing music even if the player activity gets garbage-collected, polling the Internet for RSS/Atom feed updates, and maintaining an online chat connection even if the chat client loses focus due to an incoming phone call.
Services are created when manually started (via an API call) or when some activity tries connecting to the service via interprocess communication (IPC). Services will live until no longer needed and if RAM needs to be reclaimed, or until shut down (on their own volition or because no one is using them anymore). Running for a long time isn't ...