It's a Portuguese cheese that's fairly readily available in supermarkets, at least here in the Boston area. I've attached a photo below.
The odd thing about it is, it shows up in the markets in varying degrees of firmness, from hard as a cheddar to almost spreadably soft - and that doesn't seem to be a question of age, I've frequently found batches running the full gamut of textures, all with the same sell-by date. Plus once you bring it home it's doesn't soften (or harden) further, regardless of how long you store it and whether or not you've cut into it.
The texture is key: the softer the cheese, the better the flavor. Hard ones are almost indistinguishable from domestic muenster; soft ones are lusciously rich.
Am I the only 'hound out there who's acquired a taste for it? Does anyone know anything about its background, or why it varies so much in texture?