A process running on a local or remote system that make up a purpose. In Windows for instance, services may be viewed through the Windows Task Manager.
For security and speed, it is best to have as few services running on a machine as possible. Of those services, it is important that the ones available fulfill a legitimate need, are well tested, and reliable. Newer processors continually boast better and better multi-tasking capabilities to allow many services to run concurrently.
Services that have no purpose and are just waiting to be killed are called Zombie Processes. These can be security hazards if the system is connected to a network.
TakeDown.NET -> “Service”