Compatibility is the capacity for two systems to work together without having to be altered to do so. Compatible software applications use the same data formats. For example, if word processor applications are compatible, the user should be able to open their document files in either product.
Compatibility can refer to interoperability between any two products: hardware and software, products of the same or different types, or different versions of the same product. Products that are designed to be compatible with future versions of themselves are referred to as forward compatible; products designed for compatibility with older versions are said to be backward compatible.