What does the takeoff reference speed 'V1' represent to a pilot?

1. Takeoff Decision Speed; the speed above which a takeoff must be continued even if an engine or system fails
2. Rotation Speed; the speed at which the pilot pulls back on the control column to lift the nose wheel
3. Minimum Climb Speed; the speed required to clear obstacles at the end of the runway
4. Maximum Landing Gear Extended Speed; the speed above which the landing gear must be retracted