To transfuse is to transfer blood from one person to another. If a vampire offers to transfuse your blood, say no and wait for the nurse. To transfuse also refers to instilling less physical things in people, like enthusiasm.
If you've ever lost blood, you may have needed a transfusion: blood from someone else pumped into you. When a doctor or nurse performs a transfusion, they're transfusing you. This word applies to other situations where something is being passed along. A good coach can transfuse confidence to their team. Teachers transfuse knowledge and skill. This kind of transfusing is usually a gradual process; transfusing blood is quicker.