Quote from Wikipedia:

"Abandonware is a term used to describe primarily computer software, but more recently also physical devices (which are usually computerised in some fashion) that are discontinued products and for which no product support is available, or whose copyright ownership may be unclear for various reasons. While the term has been applied largely to older games, other classes of software or equipment (such as productivity applications, utility software or mobile phones) are sometimes described as such.

Definitions of "abandoned" vary; generally it refers to a product that is no longer available for legal purchase, over the age where the product creator feels an obligation to continue to support it, or where Operating Systems or hardware platforms have evolved to such a degree that the creator feels continued support cannot be financially justified. Software companies and manufacturers may change their names, go bankrupt, enter into mergers, or cease to exist for a variety of reasons. When this happens, product rights are usually transferred to another company that may elect not to sell or support products acquired."