That's the brake pad wear warning light. Check your brake pads in the near future. Once the warning light illuminates you have a 1,000 miles or so (depending on what type of driving you do and how aggressively you drive) before the metal brake pad backing plates contact and begin scoring the rotors. When replacing the brake pads check that the rotors exceed the minimum thickness dimension stamped on the outer edge of each rotor. Rear brake pads normally last through 2 sets of front brake pads. Rotors normally last through 2 sets of brake pads ... you'll notice a lip on the outer edge of the rotors as they wear.

__________________
Fred Hoelzle