In C programming, a class is not a built-in data type, but it can be created using the keyword "class" to define a user-defined data type or data structure. A class in C++ is a user-defined type or data structure that has data and functions (also called member variables and member functions) as its members whose access is governed by the three access specifiers private, protected, or public. A class is like a blueprint for an object, and it holds its own data members and member functions, which can be accessed and used by creating an instance of that class.

In C++, a class defined with the class keyword has private members and base classes by default. A structure is a class defined with the struct keyword, and its members and base classes are public by default. In practice, structs are typically reserved for data without functions.

To create a class in C++, the class keyword is used followed by the name of the class. Inside the class, there are member variables and member functions that define the properties and behavior of the objects in a class. When a class is defined, no memory is allocated, but when it is instantiated (i.e., an object is created), memory is allocated.

In summary, a class in C is not a built-in data type, but it can be created using the keyword "class" to define a user-defined data type or data structure. A class in C++ is a user-defined type or data structure that has data and functions as its members, and it can be accessed and used by creating an instance of that class.