The point mass (aka particle) is a fictional but useful concept. However, I have yet been able to find a definition of what exactly a point mass is. It is commonly accepted that a point mass does not have an orientation, and thus only 3 coordinates to determine its position are required (as opposed to 6 coordinates required for a rigid body). Why does a point mass have no orientation? I'd appreciate it if someone can cite a definition of a point mass (if available), and show how this follows from the definition. An intuitive explanation would also be welcome.