A Lap Child is a child under two years of age at the time of departure traveling with an adult and sitting on the lap of that adult.
A “lap child” travels free on domestic flights and usually 10% of the adult fare on international flights. But, Just because you CAN fly with your infant for free on your lap, it doesn’t mean that you should. It’s interesting that the rules on traveling with a child in a car are so strict but not for flying even though the safest way to fly with an infant is in a child safety seat. The irony is that if you choose to purchase a seat for your infant and travel with a child safety seat, the FAA has a requirement for that. That’s right, no, requirement to use a child safety seat but if you do it has to be FAA approved. The question here is why wouldn’t you want to to spend the extra money for the safety of such precious cargo?