将关系数据库中的一个项与一个或多个其他项相关联

I have a list of items to be stored in a database. Each item can be associated with one or more predetermined categories. The list of categories may grow over time. What is the best way to associate one item with one or more categories (objects)? I thought about serialising the list and putting it into a single cell but this seems against the whole idea of a relational database.I have a list of items to be stored in a databa