Green’s Dictionary of Slang

a trattoria or small, Italianate restaurant, esp. fashionable in 1960s.

1969		R. Airth Snatch! xv. 149: We stopped off at a little trat Bruno knew of [...] and had a last one [OED].
1999		‘Hashing on Board’ in ‘Royal Milan & Bordighera H3 Newsletter’ on Farenheit451.it 🌐 After a hearty meal in a Tratt organised by the Capt., copious amounts of vino collapso (and a food fight) our skipper became ‘tired and emotional.’.