Part of macOS
backupdTime Machine
○ Leave it
Backs up your Mac with Time Machine.
What it is
Copies changed files to your Time Machine backup.
Why it might be busy
During a Time Machine backup. The first one takes longest. Usually minutes, or hours for a first backup.
If you stop it
The backup stops and tries again later. Leave it.
The verdict
○ Leave it. Part of macOS, or something that starts again by itself. You never need to close these.
In Activity Monitor
backupdbackupd-helper
From Procession’s guide, in the words the app shows.