You may know Traction Control by names like Automatic Stability Control (ASC) or Dynamic Traction Control (DTC). Each of these vary a bit in functionality.
Bikes with traction control have an indicator on the display that will flash when you start the bike. The flashing will continue until the bike starts rolling and the system can perform a self check. Once calibrated, the indicator will turn off. As you're riding, the system monitors front and rear wheel speed. If the rear wheel begins to spin faster than the front, say when you throttle through a patch of gravel on the road for example, the traction control will activate reducing the power applied to the rear wheel in an attempt to equalize wheel speed. When traction control intervenes, the indicator will flash rapidly. On some models, traction control can be overridden. There's a button near the grip that allows you to turn it off even when you're in motion. Simply hold down the button until this indicator lights up solid, and the traction control system is now bypassed. Hold the button down again to turn it back on.
Link to BMW Motorrad USA Video: Traction Control Basics
