LightDM: What's the difference between a seat and a session?

My background desire is to configure LightDM to display a greeter on more than one virtual terminal after boot.

That aside, I'm reading LightDM docs, the best of which I've found are repeated in numerous wikis and exemplified here:

https://wiki.parabola.nu/LightDM

I can sort of follow the default configs just fine, but what loses me is what the distinction between a seat and session is.

If I switch users, and run "dm-tool list-seats" I see one seat with two sessions and I have a session on vt7 and a session on vt8.

And yet the only clues I find on-line from people having asked about same seem to duplicate seats:

• How to enable second x session on tty8 in 14.04
• https://unix.stackexchange.com/questions/87169/autostart-all-lightdm-seats-and-show-one-as-default

and it seems to me, to a basic element missing from the documentation underpinning this: what is a seat and what is a session and how do they differ?

The corollary is:

Can we configure lightdm to start

1. one seat with two sessions (on vt7 and vt8 say), or
2. two seats with one session each (on vt7 and vt8 say)

It would be nice if this were better documented and if the fancy takes me I'll file an issue asking for it here:

https://github.com/CanonicalLtd/lightdm