Training wheels are small extra wheels attached to the back of a bicycle to help someone learn to ride without falling over. They stick out on both sides and touch the ground when the bike starts to tip, catching you before you lose your balance.

When you're first learning to ride a bike, balancing feels almost impossible. Your body hasn't yet learned the dozens of tiny adjustments needed to stay upright. Training wheels let you focus on pedaling and steering while they handle the balance part. As you get more confident, someone can gradually raise the training wheels higher off the ground so you start doing more of the balancing yourself.

Eventually comes that exciting (and slightly scary) day when the training wheels come off completely. You might wobble and fall a few times, but soon your body figures out the balance, and you're riding on your own.

People also use “training wheels” as a metaphor for any kind of extra support that helps you learn something difficult. A beginning guitarist might say that playing simpler songs is like using training wheels before attempting complicated solos. A new coder might use training-wheels software that catches errors and offers hints. The idea is always the same: temporary support that helps you build skills until you're ready to try it on your own.