The entire drive must be done autonomously, under its own propulsion, with no human input. Humans can help with any parts other than driving and navigation, such as fueling/charging the car and performing repairs. The original route can be chosen by a human, but after that, any updates to the route due to road closures, heavy traffic, running out of gas and needing to go to a gas station, etc. must be decided on by the car.

The car must not break any traffic laws that could reasonably get a human driver in trouble. (e.g. if it sees an object in the road and chooses to swerve into an empty opposite-direction lane in order to avoid the object, that's fine.) Other road-related laws that don't have to do with driving capablity, such as an expired registration, won't disqualify the car. It also must not engage in any behavior that is legal but still highly unsafe, such as running into a pedestrian who's in the road illegally without a crosswalk.

If's fine if there's a human physically inside the car, they just can't provide any control inputs. If a human driver has to take over even once, such as to avoid an unexpected dangerous situation or help the car navigate through a complicated construction area, that disqualifies the trip.

Remote human driving, such as a human in an office looking at sensor feeds and driving the car from there, does not count as "self-driving".