Disco fries are French fries, served with gravy and cheese.
The gravy is often chicken gravy.
The cheese used is mostly American processed cheese.
Some restaurants offer fancy versions, with a Brie and truffle cheese sauce, or sweet-potato fries topped with clam chowder, cheese and jalapeno peppers.
Disco fries are a specialty of the American east coast from Odessa, New York down to Atlanta. Their home state appears to be New Jersey, though not everyone in New Jersey would know them by that name.
No one seems entirely sure why they’re called “disco fries.”
At the Big Steer Travel Center (near Northfield, Minnesota, on Highway 19 just west of Interstate 35), what they call disco fries are round potato wedges — potatoes sliced thickly cross-wise (instead of length-wise) to make round discs. There does not appear, however, to have ever been any gravy or cheese on them.
Disco Fries are also made in Glasgow, Scotland, though they do not use that name for them or have any special name for “chips with fries and cheese” on them.