The term "birthfather" refers to the biological father of a child who has either relinquished their parental rights or was not involved in the child's upbringing. However, there are alternative terms that can be used depending on the context. "Biological father" is an alternative term that simply refers to the genetic relationship between the father and child. "Sperm donor" is a term that specifically refers to a father who has donated sperm to conceive a child outside of sexual intercourse. "Natural father" can also be used to refer to the biological father, although it may imply a certain level of legitimacy or authority over the child.