Extraversion and introversion
Picture this...
You are arriving early for the first day of a new job. When you enter the department, you notice a quiet man collecting a pile of notes and making for one of the rooms off the reception area. His eyes alight on you briefly as he does so; he nods, and there is a brief smile.
Long enough to be polite, but not to encourage. He vanishes. You look around for someone who might help you, and you notice a woman behind the reception desk. You move towards her, and before you can speak she beams at you, and asks if she can help.
You explain who you are and she beams another welcome, and proceeds to tell you who you should see, when they are likely to arrive, where the toilets are, how to get lunch, who your secretary will be, what the boss is like, and where she went for her holidays.