The correct answer is: B. It defines the appearance and behavior of an object.
A class definition is a blueprint for creating objects. It defines the properties and methods that an object of that class will have. When you create an object, you are essentially creating a new instance of the class.
The appearance of an object is determined by its properties. Properties are variables that belong to an object. They can be used to store data about the object. For example, a car object might have properties for its color, make, and model.
The behavior of an object is determined by its methods. Methods are functions that belong to an object. They can be used to perform actions on the object. For example, a car object might have methods for driving, parking, and refueling.
Option A is incorrect because an object is an instance of a class. A class is a blueprint for creating objects.
Option C is incorrect because a namespace is a way of grouping related classes together.
Option D is incorrect because a prototype is an object that is used to create other objects.