Fullcoat is Mag Stock with a layer of oxide that completely covers one side, unlike Stripe. All 16mm mag is fullcoat. 35mm is available in both fullcoat and stripe. The difference in 35mm is that fullcoat can be used for recording several tracks, and it typically used for the Mix Master. Fullcoat is also more expensive than stripe.
The Pollio Folio - Glossary of Cinematography Terms