In Juju, a base is a way to identify a particular operating system (OS) image for a Juju machine. This can be done via the name of the OS followed by the @ symbol and the channel of the OS that you want to target, specified in terms of <track> or, optionally, <track>/<risk>. For example, ubuntu@22.04 or ubuntu@22.04/stable.

Starting with Juju 3.1, a base replaces the older notion of series.