A person is on the witness stand. He has an adopted child under 18 but no biological kids. He is asked if he is a parent. He says no. Did he commit perjury?
A person is guilty of perjury, a crime of the third degree, if in any official proceeding he makes a false statement under oath or equivalent affirmation, or swears or affirms the truth of a statement previously made, when the statement is material and he does not believe it to be true.
The Code also provides an opportunity for retraction.
Assuming that the statement is material, whether answering "no" is perjury will depend on the witness's understanding of the question and his belief about the truth of the answer.
If we assume that the witness understands the question to be about parentage in general, including by adoption, and if we assume that they know they have an adopted child, the answer "no" would be perjury.
If instead we assume that the witness understood the question to be narrowly about biological parentage, or if they had forgotten at the time of their answer that they had an adopted child, then the answer "no" would not be perjury.
No, it is not perjury. Analogously, "It depends on what the meaning of the word 'is' is" (Clinton testimony). In Bronston v. United States, 409 U.S. 352 it was held that
There is no liability for perjury if a person gives truthful information in responses to questions made under oath, even if the information was intended to mislead the questioner
The person posing the question has the duty to ask the precise question, and cannot impose a duty on the witness to guess at the exact intended meaning or ask for clarification. There is a clear definition of "parent" which sees "parent" as a biological relationship, therefore the person interrogating the witness must clarify whether it includes adoptive relations, or whether it includes a terminated legal parent relation ("put up for adoption").