For a definition:

http://en.wikipedia.org/wiki/Core_competency

A competency can be identified as a demonstrable trait that is considered important for success in a field. The underlying knowledge is assumed if the competency is demonstrated. Those actions that speak louder than the words are associated with competency.

Competence is defined as: the habitual and judicious use of communication, knowledge, technical skills, clinical reasoning, emotions, values and reflection in daily practice for the benefit of the individual and the community being served.

Competence therefore is not an absolute, nor does it involve a narrow set of professional behaviours; rather competence reflects sufficiency on a broad spectrum of personal and professional abilities relative to a given requirement.