Explain what the term 'pure virtual method' means in object-oriented programming.

A pure virtual method is a method in a base class that has no implementation and must be overridden in derived classes. In C++, it is declared with = 0 in the method declaration. A class containing at least one pure virtual method becomes abstract and cannot be instantiated.

Example:

class Shape {
public:
    virtual void draw() = 0; // pure virtual method
};

class Circle : public Shape {
public:
    void draw() override {
        // implementation of circle drawing
    }
};

This allows creating interfaces and ensuring polymorphism, forcing inheritors to implement the necessary methods.