In Java, a package is a namespace used to organize classes and interfaces in a hierarchical manner. It allows developers to group related classes, interfaces, and sub-packages, making the code easier to manage and avoid naming conflicts. Packages can be categorized as either built-in (such as java.util, java.io) or user-defined. By organizing classes into packages, Java ensures a more modular and maintainable structure. Additionally, packages provide access control, as classes within the same package can access each other's members more freely than those in different packages. To use a package, the import statement is used to bring specific classes or entire packages into scope.