Comment 5 for bug 1637861

GNOME Software (branded as Ubuntu Software in Ubuntu) installs / removes applications (defined below). Applications come from the Ubuntu archives or the snap store (confusingly this currently allows non-graphical snaps, but I consider that a bug to fix). It also provides firmware updates. While GNOME Software does have a mechanism to do updates, the primary interface for updates is Update Manager.

An application is required to have:
 - A .desktop file (so the shell can launch it)
 - Suitable metadata (this is why some traditional Debian packages might not show).

The description you linked to seems accurate to me.