Four points can define a hyperplane in four-dimensional space, but they do not necessarily define a three-dimensional plane if they are not coplanar. Similarly, three points can define a three-dimensional plane, but they may not always be collinear, meaning they do not necessarily define a line. The discussion highlights the importance of point arrangement in determining dimensionality. Understanding these relationships is crucial in geometry and higher-dimensional mathematics. The conversation emphasizes the nuances of point configuration in defining geometric structures.