why we call varable as on object here
In C++, a variable is often referred to as an object because it is an instance of a class or a struct. A class or struct defines the behavior and properties of an object, and a variable of that class or struct type is an instance of that object.

For example, consider the following class:

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class MyClass {
    public:
        int x;
        void print() {
            std::cout << "x = " << x << std::endl;
        }
};
This class defines a simple object that has a single member variable x and a single member function print(). To create an instance of this object, you would create a variable of type MyClass:

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MyClass myObject;
This variable myObject is an instance of the MyClass object. It has its own copy of the member variable x and can call the member function print().

This concept applies to the unique_ptr and shared_ptr objects as well, they are instances of the unique_ptr and shared_ptr classes, respectively, and they are used to manage the memory and ownership of the objects they are pointing to.

It's worth noting that "object" in C++ is a term that can be used in multiple contexts, and it could refer to different things, but in the context of this discussion, we're using it to refer to an instance of a class or a struct.