Sensitivity (also called recall rate in some fields) measures the proportion of actual positives which are correctly identified as such (e.g. the percentage of sick people who are correctly identified as having the condition). Specificity measures the proportion of negatives which are correctly identified (e.g. the percentage of healthy people who are correctly identified as not having the condition).
K. McCarthy, B. Zabar, and G. Weiss. Proceedings of the 1st international workshop on Utility-based data mining, page 69--77. New York, NY, USA, ACM, (2005)
R. Kanawati, and M. Malek. AAMAS '02: Proceedings of the first international joint conference on Autonomous agents and multiagent systems, page 1137--1138. New York, NY, USA, ACM Press, (2002)