Charisma has three parts:
1) Having a very strong, unique and interesting identity that is easily conveyed to other people with little explanation.
2) Being able to connect this identity with the identity of whoever you meet.
3) Having the excellent social skills to do this subtly and efficiently.
If you want an analogy, #1 is like having an excellent and unique product. #2 is being able to market that product to everyone in ways they understand and appreciate. #3 is appropriately using the mediums of communication to transmit this marketing.
That is charisma.