The brushed electric motor is generally the only kind of motor found in toy-grade and beginner hobby-grade RCs. Kits and other hobby-grade RCs still commonly used brushed motors although brushless is becoming more readily available. Small contact brushes inside the motor cause the motor to spin. Brushed motors come in fixed and nonfixed versions. Electric motors with fixed brushes are nonadjustable and can't be modified or tuned. Nonfixed brushed motors have replaceable brushes and the motor can be modified and tuned to a certain degree as well as being cleaned of dust and debris that accumulates during frequent use.
Becoming increasingly popular in the RC hobby, brushless electric motors are still slightly high-priced compared to brushed motors. They are only just now becoming legal in some professional RC racing circuits. The appeal of brushless motors is the sheer power they can give to your electric RC. Brushless motors, as the name implies, do not have contact brushes, don't require frequent cleaning, and because there are no brushes there is less friction and less heat -- the number one killer in motor performance.
Brushless motors can also handle a lot higher voltage than brushed motors. With a high voltage supply brushless motors can help a beginner RC race at blistering speeds. RCs equipped with brushless motors currently hold the fastest speed records for RC -- yes, faster than nitro.