ticket vs billet

3.4 Going on The Tram ou à Bord du Tramway:

Is there a difference between ticket and billet in public transportation term aside from the lesson? Beginner question again.

Hmm...good question. It's ticket for the métro in Paris and also for the cinéma. But it's billet for the SNCF (regional train) and navettes (shuttles). And I'd say all the museum-type passes are billet also (at least from experience).

From observation, I would guess that it's a combination of small physical size and price that makes it a ticket. But really, whatever the dispenser says when I'm paying is what I'd call it. :)