User-Centered Design (UCD) is:
"...the process of designing a tool, such as a website's or appliations user interface, from the perspective of how it will be understood and used by a human user."
User Experience Design (UXD) is:
"...entails conducting user research exercises with intended users of system...[in order] to accommodate and support user behaviors in a way that users will experience as naturak and satisfying."
From "Introduction to User-Centered Design", http://www.usabilityfirst.com/about-usability/introduction-to-user-centered-design/