Objectives  In view of the lack of complete definition, confusion about denotation of basic concepts of waterjet and pumpjet and confusion of product appellations both at home and abroad at present,

  Methods  the common and special characteristics of the two propulsors were refined out and their differences distinguished based on the analysis of their working principle and concrete structures, the definitions of waterjet propulsion and pumpjet propulsion were proposed and their common characteristics, special characteristics and differences were pointed out.

  Results  The waterjet and pumpjet are all pump-type propulsors, all of which rely on the matching design of rotors and stators on the flow field inside a duct to produce an axial jet. The first design index of waterjet is high efficiency and the rapidity shall be ensured primarily, whose design result is a waterjet. The first design index of pumpjet is low noise (the acoustic stealth)shall be ensured primarily, whose design result is a pumpjet.

  Conclusions  This definition not only includes and distinguishes all existing waterjets and pumpjets, but also points out the problems of some foreign pump-type propulsor's nomenclature and classification. This definition helps the public understand and distinguish between waterjet propulsion and pumpjet propulsion.