Custom is used to refer to something considered normal or polite in other countries or in other times. Tradition is used to refer to something that has existed for many years, and it has been passed down from previous generations.
custom The Japanese have the custom of taking off their shoes before entering the house. The tour guide explained the local customs.
tradition There are many ancient traditions in Japan. His sons followed the family tradition and became lawyers too. It’s a tradition in our family for all first-born males to be called Charles.