I am looking at some document on the web about background task and background fetch.
Background task is a task which performance at the background while the app still running. When the app is in the background, the task have a limited time to get the task done, once it's fully background, the task have to be ended as well.
Background Fetch is the where the application is fully in background or inactive, the action will be scheduled to be executed at some point in time if the resources available.
This was my very brief understanding.