Christmas disease is another name for : -

Haemophilia is an X-linked recessive disorder in which blood fails to clot normally.
Haemophilia A is due to deficiency of clotting factor VIII (antihaemophilic globulin).
Haemophilia B is due to deficiency of clotting factor IX (Christmas factor). It is called Christmas disease after Stephen Christmas, the first patient in whom it was described (1952).
So Christmas disease is another name for haemophilia B.