A service is a long-running system-managed process that usually works in the background.
People often restart or kill services without realizing they are system-managed workloads with dependencies, logs, and restart rules.
A service is background software the operating system expects to keep available over time, often without a visible window.
A service is a helper program that keeps doing its job in the background, even when you are not looking at it.
A service is still a process, but it is usually managed more deliberately by the operating system or service manager.
Services often start automatically, write logs, and may restart when they fail. That is why troubleshooting a service is different from simply closing an app window.
Study the larger concept after the word itself becomes clear.