Service is like an Activity but has no interface. For example, for fetching information on weather, blank activity will not be created. Here Service will be used. It is also known as Background Service because it performs tasks in background.
A Thread is a concurrent unit of execution. Take note that the UI cannot be updated from a Thread. For this a Handler must be used.
If you want to explore more, visit our Android edu & tutorials section! Below are some examples:
Learn how to build Android apps:
Invoice to PDF in Android