A "hobby" is a special interest or activity that you do in your time off. Some people have animals as hobbies. They keep rabbits, or go fishing. They train dogs to do tricks, or keep pigeons to race and carry messages. Some are crazy about plants. They try to grow cacti or rare tropical flowers in their kitchens and sitting rooms.
Others are mad about their car or their motorbike. They spend their Saturdays and Sundays washing them, painting them, or buying new bits and pieces to make them go even faster.
Children and teenagers are great collectors. They collect stamps, or postcards or matchboxes, or pictures of a favourite footballer or pop star.
Many people make things as a hobby. Some teach themselves at home, but a lot of people go to evening classes at their local college. Just look under letter B in a list of London or New York evening classes and you'll find: Ballet, Batik, Bengali, Body building, Breadmaking and Byzantium.
But not everyone goes to evening classes to learn about his special interest. No one helped these people to do what they did.
A "hobby" is usually something that a person does alone. But American (and British) families sometimes like to do things together too.