Essentially, this refers to the motor installed in the remote control car and applies to hobby grade models rather than toy grade. It really is as straight forward as brushed motors have brushes where as a brushless motor does not.
A brushless motor is ultimately more powerful than a brushed motor which makes for a faster remote control motor. Brushless motors do also tend to be a little more durable than brushed motors.
Remote control models with brushed motors are aimed towards beginners and older children whereas brushless models are designed for intermediate and experienced hobby grade users.
For more information, check out our blog post https://www.rcgeeks.co.uk/blogs/news/what-are-brushless-rc-cars.