This paper is a survey of some recent developments in the study of extending modules. The idea is to examine the behavior of closed submodules in the theory and separate it from complement submodules as much as we could. Main focus is on all different definitions of extending modules in the area but which are only based on closed submodules and  condition. Finally, we give some classifications of all extending modules under the three different figures.

closed submodule, essential submodule, extending module, module classes, torsion theory.