Part of macOS

`nsurlsessiond`Background downloads

○ Leave it

Downloads and uploads for apps in the background.

What it is

Apps hand long downloads and uploads to this service so they can finish later.

Why it might be busy

An app or iCloud is moving a lot of data. Usually until the transfer finishes.

If you stop it

macOS starts it again straight away. Leave it.

○ Leave it. Part of macOS, or something that starts again by itself. You never need to close these.

From Procession’s guide, in the words the app shows.