A more thorough explanation:

Legitimacy presumption is a legal concept in family law that assumes the father of a child is the man who meets certain criteria. These criteria include:

• Being married to the child's mother when the child was conceived or born, even if the marriage was invalid
• Marrying the mother after the child's birth and agreeing to have his name on the birth certificate or to support the child
• Welcoming the child into his home and later holding out the child as his own

For example, if a married couple has a child, the husband is presumed to be the father of the child. This presumption can be challenged, but it is the starting point for determining paternity in many cases.

The legitimacy presumption is also known as the presumption of paternity, presumption of legitimacy, or paternity presumption.