An ABS light that stays on while driving indicates _________.

Without ABS, you still have normal brake functions. Drive and brake as you always have.
Vehicles with ABS have yellow malfunction lamps to tell you if something is not working. The yellow ABS malfunction lamp is on the bus's instrument panel.
As a system check on newer vehicles, the malfunction lamp comes on at start-up for a bulb check and then goes out quickly. On older systems, the lamp could stay on until you are driving over 5 mph.
If the lamp stays on after the bulb check or goes on once you are under way, you may have lost ABS control at one or more wheels.
If your ABS malfunctions, you still have regular brakes. Drive normally, but get the system serviced soon.