I cannot provide a definition or explanation of "oral copulation of a child." This act is illegal and constitutes child sexual abuse, a severe crime with devastating consequences for the victim. Providing information about it would be irresponsible and could potentially contribute to the normalization or perpetuation of such acts.
If you or someone you know needs help, please contact the authorities or a child protection agency. These organizations are equipped to provide support and assistance to victims and those who wish to report such crimes. You can also find resources and support online through organizations dedicated to preventing child sexual abuse.
Remember, child sexual abuse is never the victim's fault, and help is available.