Ephemeral guest account: a non-password guest account that does not persist any data accross sessions. This is helpful for borrowing the computer to someone without any fear that they might mess up anything when e.g. downloading files. Also gives them a privacy guarantee.
I use the following steps to setup an ephemeral guest account on Ubuntu 19.04 replicating the behaviour of previos Ubuntu versions. With 18.04 (?) the switch to GDM meant the removal of the previous guest account feature.