Many of the terms dealt with by roboticists such as consciousness, emotion, and intelligences are notoriously difficult to define. Researchers Shane Legg and Marcus Hutter have put together a very interesting collection of over 70 definitions of intelligence (PDF format), creating the largest and most well-referenced such collection to date. With a little effort, I bet we could expand their list to twice the size! They've divided the list into collective definitions, psychologist's definitions, and AI researcher's definitions. Among the definers you'll find Minsky, Schank, Warwick, Lenat, Feigenbaum and other well-known AI and robotics researchers. Definitely worth a read if this is a topic you wrangle with when designing your robots.