A hobby is an activity that someone does for fun when they are not working. Different people have different hobbies. Some people like dancing whereas others like cooking, playing cards, reading books etc. Hobbies always change as interests and fashions change.
When I was a child, my dad used to bring me coins from different eras of India as well as abroad. I had wooden boxes to store them, collect information for each of them, maintain a logbook and clean them every once in a while. I had an impressive coin collection.
As I grew up a bit more to find an interest in sports. I loved swimming. I picked up various styles to swim. Then I had a habit of reading books, novels, fiction also and so on. As I grew up my hobbies also changes. Nowadays my favorite hobby is traveling. I love to visit new places especially hills areas for tracking. Not just visiting but the journey itself was such an adventurous one for me.