Proprietary lock-in is the practice of different companies creating different versions of the same system architecture that can't interoperate. The purpose is to make it difficult for users to switch to competing systems. Typical were the EBCDIC character set by IBM, the desktop wars among Unix vendors, the several slightly different implementations of various open standards, and more recently the shift from Xenix to MS Windows NT by Microsoft.
This is also practiced by manufacturers who design their products so that replacement parts or add-on enhancements must be purchased from the same manufacturer, rather than from a third party.
See also: Vendor lock-in.