The Sacral chakra is about feeling and sexuality. When it is open, your feelings flow freely, and are expressed without you being over-emotional. You are open to intimacy and you can be passionate and lively. You have no problems dealing with your sexuality.
If you tend to be stiff and unemotional or have a "poker face," the Sacral chakra is under-active. You're not very open to people.
If this chakra is over-active, you tend to be emotional all the time. You'll feel emotionally attached to people and you can be very sexual.