Conscientiousness is one of the five personality traits described in the Big Five model of personality psychology. It's used to describe a person's tendency to be organized and goal-oriented.
Someone with a high degree of conscientiousness is self-disciplined, efficient, orderly and methodical. They place a lot of importance on getting stuff done - and getting it done properly. They turn up on time, meet deadlines and follow the rules.
It's hardly the most tantalizing trait in the pack.