This refers to a situation where the sperm used for fertilizing the egg, does not belong to the male partner but is actually donated from someone else. Following are some cases where donor sperm is required:
Donor sperm can be collected either from a sperm bank, or could be provided by a relative, or friend or an anonymous donor.
Under this situation, the eggs used for insemination does not belong to the person in whose uterus they will be placed after fertilization, rather they are donated by someone else. Cases where donor oocytes can be needed:
Donor oocytes are usually provided by someone who is genetically related however they can be donated by someone else too.