Final answer:
Penal Code 25.03 states that an offense occurs when a person knowingly retains a child under 18 contrary to the terms of a custody order or judgment. This is known as interference with child custody and is a serious legal offense.
Step-by-step explanation:
According to Penal Code 25.03, an offense is committed when a person knowingly retains a child younger than 18 in violation of the express terms of a judgment. This can refer to cases where there is a custody order in place, and one parent keeps the child beyond the time allowed by the court order. It is a serious offense that often arises in cases involving child custody disputes. Legally, this is known as interference with child custody. The law aims to prevent a parent or guardian from unlawfully taking or keeping a child against the terms set out by the court, thus ensuring the child's well-being and adherence to the legal custody agreements.