What is a COPY CONSTRUCTOR and when is it called?

A copy constructor is a method that accepts an object of the same class and copies it's data members to the object on the left part of assignement:
class Point2D{ int x; int y;
public int color;
protected bool pinned;
public Point2D() : x(0), y(0) {} //default (no argument) constructor
public Point2D( const Point2D & );
};
Point2D::Point2D( const Point2D & p )
{
this->x = p.x; this->y = p.y; this->color = p. color; this->pinned = p.pinned;
}
main(){
Point2D MyPoint;
MyPoint.color = 345;
Point2D AnotherPoint = Point2D( MyPoint); // now AnotherPoint has color = 345