All radar targets can be classified into point and complex targets. A point target is a convenient model object commonly used in radar science and practice to solve certain types of problems. It is defined as a target located at distance R from a radar at the viewing point '0', which scatters the incident radar radiation isotropically. For such a target, the equiphase surface is a sphere with the centre at '0'. In practice, most radar targets refer to the class of complex targets. In spite of a great variety of particular targets, we can offer a common criterion for their classification. This criterion is based on the relationship between the maximum target size and the radar resolving power in the coordinate space of the parameters R, a, β and R, which are the range, the azimuth, the elevation angle and the radial velocity of the target, respectively.