Here's a very niche question. If someone were to have completed their recreational or sport pilot license and be actively pursuing their private pilot license, could flight time without an instructor but with a passenger on board (allowed because the pilot in question has their sport/recreational) be logged as solo? It's a weird question with no real cause, but it was something I was thinking about and I couldn't figure it out myself.
No, solo means you're alone in the aircraft. 14 CFR 61.51(d) says:
Except for a student pilot performing the duties of pilot in command of an airship requiring more than one pilot flight crewmember, a pilot may log as solo flight time only that flight time when the pilot is the sole occupant of the aircraft.