An americano is indeed an espresso (sometimes double shot) with added hot water. Not Italy specific though, it’s just a different thing than filter coffee - but it’s true that in Italy you can usually get the former but not the latter.

Some other common coffees: lungo (“long”, an espresso that’s extracted for longer so it’s a bit more “watery”), macchiato (“stained”, an espresso with a bit of milk and foam in it, kinda like an espresso version of a cappuccino), macchiatone (“big macchiato”, halfway between macchiato and cappuccino), corretto (“corrected”, with a tiny bit of liquor, usually grappa or sambuca)