Training wheels are an accessory used to help children learn how to ride a bicycle. They are typically two small wheels attached to the rear axle of the bike, and provide stability and support while the child learns how to balance and pedal. The term 'training wheels' is often used as a metaphor for any kind of support or guidance given to someone who is learning a new skill. The crossword solution for the term 'training wheels' is RAILCAR, which is a vehicle used to transport passengers or freight on a railway.