Wikipedia: Presumption of paternity in paternity law and common law is the legal determination that a man is "presumed to be" a child's biological father without additional supportive evidence, usually as a result of marriage.

Please note:

An acknowledgement of Paternity (AOP) is a legal form signed by a man and the child's mother that states (under penalty of perjury) that the man is the child's genetic father. An AOP is usually used when the parents aren't married but agree on the identity of the child's father.

Note also:

Recognition is the process in some jurisdictions whereby a man is recognized as the father of a child in situations where there is no presumption of paternity, generally due to the mother being unwed.