Foreign Black-Bordered (FBB) Core Sets are foreign black bordered editions of Revised and Fourth Edition.
Since 1994 Magic cards are produced in other languages than English. The original release of a Core Set in a new language was usually black bordered, and is thus easily identifiable. Hence French, German, and Italian black bordered cards without an expansion symbol are from the language's Revised Edition. Black Bordered cards in Chinese (traditional), Japanese, Portuguese, and Spanish are from Fourth Edition as production of these languages started only after Revised went out of print. There are also comparable black bordered Russian cards, but these have the Ninth Edition expansion symbol. Only Chinese (simplified) doesn't have an original black bordered release.
Cards from these sets are usually highly sought after and thus rather expensive. The dual lands from the black bordered Revised Editions are particularly valuable as they are the only alternative to expensive Alpha/Beta dual lands for a player that wants to play black-bordered cards.
The first black bordered printing in a foreign language was in some cases immediately followed by a white bordered printing of the same set.