A baby born on US soil to a woman intentionally brought here so that the baby will be a US Citizen, in the expectation of raising it to be a Muslimterrorist.
There are, of course, a few problems with this definition:
1. Nobody has ever shown any evidence that anybody is having such babies. (Any assertion is true of the empty set...)
2. The creators of such a baby would have to wait 12 years or so before it would be old enough to be an effective terrorist. Compare this with the effort of recruiting a terrorist from existing US citizens who are already Muslims or can be converted to Islam.