Java class is the basic concept of object-oriented programming language. Java class is a user-defined template or blueprint where objects, data members and methods are defined and a set of instructions to build a specific type of object. The variables and methods of the same Java class are common for all the objects of the class.
In Java, the class keyword is used to define a Java class.

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https://www.c-sharpcorner.com/article/a-complete-java-classes-tutorial/

Class : class can be defined as a template/blueprint that describes the behavior/state that the object of its type support.
One can simply called as a user define datatype.

Types of classes
POJO Class
Static Class
Concrete Class
Abstract Class
Final Class
Inner Class
Nested Inner class
Method Local inner classes
Anonymous inner classes
Static nested classes