C++ - What is object slicing?

# include <iostream>
# include<string>
using namespace std;

class Base
{
public:
	virtual string print() const
	{
		return "This is Base class";
	}
};

class Derived : public Base
{
public:
	virtual string print() const
	{
		return "This is Derived class";
	}
};

void describe(Base p)  <--- Object Slicing Here.
{
	cout << p.print() << endl;
}

int main()
{
	Base b;
	Derived d;
	describe(b);
	describe(d);
	return 0;
}

Output

This is Base class
This is Base class