The take-off roll, also called ground roll, is the roll distance before the aircraft becomes airborne.
In case of the 737-900ER, it will be in the order of 2000 meter.
The quoted 3000 meter is probably the take-off distance required (TODR) or take-off run required (TORR) at maximum take off weight. That assumes a full throttle acceleration to about half of the runway (1500 m), then an engine failure, continued acceleration on a single engine, rotation and take-off at 3000m. In case of TODR, the climb to a height of 35 ft is included as well (for FAR Part 23 aircraft it is 50 ft).
This means the 737-900ER requires a runway of 3000 meter length to take-off with an engine failure or to stop when the failure happens before the decision speed (V1). Since engine failures are unpredictable this is the minimum runway length required for take-off planning.
This all assumes ICAO standard atmosphere conditions. For runways at higher altitude ( > MSL) / higher temperature (> 15 deg C) the TORR will be even higher.