Although an introductory paragraph is fairly graphic and specific, the following text is the formal definition, which seems like it could be more broadly interpreted. See the essay that I linked above.

CHAPTER 74 -- PARTIAL-BIRTH ABORTIONS
"Sec.
"1531. Partial-birth abortions prohibited

§1531. Partial-birth abortions prohibited

       (a) Any physician who, in or affecting interstate or foreign commerce, knowingly performs a partial-birth abortion and thereby kills a human fetus shall be fined under this title or imprisoned not more than 2 years, or both. This subsection does not apply to a partial-birth abortion that is necessary to save the life of a mother whose life is endangered by a physical disorder, physical illness, or physical injury, including a life-endangering physical condition caused by or arising from the pregnancy itself. This subsection takes effect 1 day after the date of enactment of this chapter.

       (b) As used in this section --

(1) the term 'partial-birth abortion' means an abortion in which --

                   (A) the person performing the abortion deliberately and intentionally vaginally delivers a living fetus until, in the case of a head-first presentation, the entire fetal head is outside the body of the mother, or, in the case of breech presentation, any part of the fetal trunk past the navel is outside the body of the mother for the purpose of performing an overt act that theperson knows will kill the partially delivered living fetus; and

                   (B) performs the overt act, other than completion of delivery, that kills the partially delivered living fetus; and