In contemporary personality theories, a "Type B personality" means someone is generally laid back and steady in performance. The "Type B" is often simply viewed as a counter to the popular "Type A personality," which describes a person who is intense and accomplishment-driven.
Type B people tend to operate at a lower stress level because they aren't as obsessed with accomplishment and deadlines. Many B-personality types are successful, but they aren't as motivated by the thrill of success. This approach may leader to longer-lasting enjoyment of achievements. Though studies vary in results, Type B personalities are also seen as less aggressive than Type A people.