What is object slicing?

using namespace std;

class Base {
public:
    void printBase(){
        cout << "print Base" << endl;
    }
};

class Child : public Base {
public:
    void printChild(){
        cout << "print Base" << endl;
    }

};

int main()
{
    Child *childPtr = new Child();
    Base *basePtr = childPtr;

    cout << "childPtr : " << childPtr << ", basePtr : " << basePtr << endl;
    childPtr->printBase(); // possible
    childPtr->printChild(); // possible

    basePtr->printBase(); // possible
    //basePtr->printChild(); //Not possible

}

childPtr : 0x100100e20, basePtr : 0x100100e20
print Base
print Child
print Base
Program ended with exit code: 0