Xbase "Generic term for the dBASE family of database languages. Coined in response to threatened litigation over use of the copyrighted trademark 'dBASE'."
Xbase is a complex of data files (.DBF), indexes (NDX, MDX, CDX etc.) and eventually note files (DBT) for storing large amounts of formatted data in a structured form.
The Xbase family of databases is covering the dBase, Clipper, FoxPro, and their Windows equivalents Visual dBase, Visual Objects, and Visual FoxPro, plus some older products. All are based on the .DBF file format.