A Supply Chain is a system of organizations, people, activities, information and resources, for creating and moving products including product components and/or services from suppliers through to their customers.
Supply Chain Risks is the intersection of threats to supply chains (which can be geological (i.e.: winter storm), physical (fire or flood), or cyber-based (hacking event shutting down a supplier) and the vulnerabilities you have inherent in your business (i.e.: a sole supplier of a critical component).
Source: CNSSI 4009, NIST SP 800-53 Rev 4