Allogenic bone marrow transplant means stem cells extracted from another person. "Donor" is the person whose stem cells have been extracted. Often, the donor genes (partial/whole) must match the patient's genes. Specially designed tests (HLA tests) are done to determine if a donor is a good match for the patient. The donor could be from family but it isn't mandatory. In many cases, the donor isn't related to the patient at all. There are many national/international bone marrow registries where people can find ideal match donors who are unrelated to them but still compatible.