When is an aircraft considered a departure?

Talking to my coworkers, and we were talking about when an aircraft is considered a departure for the departure time. They said it’s when it crosses the threshold, and I said when it is airborne. I’ve looked in the .65 and for low approaches it’s considered a departure after the landing threshold, but in the glossary it says departure time is when the aircraft is airborne, and it’s airborne when all parts of the aircraft is off the ground. Which is correct?