Flying and landing the same vehicle multiple times per day, without significant refurbishment between flights — the operational threshold that separates SpaceX from every other launch program.
Tensions
Most discussion of "reusability" conflates two regimes: refurb-and-refly (30-60 days, achievable by several entrants over the next decade) versus rapid reusability (turn-the-rocket-around-in-hours, required for Moon/Mars logistics and orbital compute). Treating them as the same metric understates SpaceX's lead.