Different manufacturers call it different things. Whether you call it ECM, BCM, PCM, TCM or something else, they all mean pretty much the same thing. It's your car's computer. Computers hold information and that information can be changed in a way that effects the performance of the vehicle. You can change just about any part of the vehicle performance from gas mileage to how the transmission shifts.
Of course the ability to do all these nifty modifications requires specialized equipment and training. Although the cost varies depending on what you want done, it is very affordable today and it's mobile. You don't even have to bring your car to me. I can go to you and do this in your driveway.
Service limited to Ford, GM, and Chrysler.