Which term correctly completes the phrase: "When Galileo created the idea of ballistics ______, his equations did not include drag nor gravity."

The term that accurately completes the phrase is "Parabola." When Galileo developed his ideas about ballistics, he described the motion of projectiles as following a parabolic path, which arises from the influence of initial velocity and the effects of gravity in a vacuum. His equations of motion inherently simplify the situation by not accounting for drag or other forces, thereby assuming an idealized scenario where the trajectory takes the shape of a parabola.

While "arc," "path," and "trajectory" are related terms, they do not specifically denote the mathematical representation that Galileo was focusing on. "Parabola" specifically captures the nature of the motion as mathematically modeled in projectile motion, making it the most precise choice in this context.