A more thorough explanation:

Definition: An illegitimate child is a child who was not conceived or born in lawful wedlock, nor later legitimated.

At common law, such a child was considered the child of nobody and had no name except one that was gained by reputation. Being no one's child, an illegitimate child could not inherit, even from the mother, but all states now allow maternal inheritance. Full paternal inheritance is permitted if the child can prove paternity in accordance with state law. This burden of proof, uniquely imposed on an illegitimate child, is constitutionally permissible.

Example: A child born to unmarried parents is considered an illegitimate child. In the past, illegitimate children were not entitled to the same legal rights as legitimate children, but now most states have eliminated this distinction.

Explanation: The example illustrates that an illegitimate child is a child born to unmarried parents. It also shows that in the past, illegitimate children were not treated equally under the law, but now most states have eliminated this distinction and granted them the same legal rights as legitimate children.