2D materials are a class of materials with only one dimension in nanoscale. Due to the increase in the number of surface atoms in two-dimensional materials, the physical and chemical reactivity compared to the bulk counterpart significantly increased. 2D materials characteristics such as high anisotropy, high surface area, unique morphology, and tunable mechanical, optical, electrical, and magnetic functionalities come out to be a fascinating candidate for application in electro-optical and electronic devices, energy and environmental fields, as well as biomedical and drug delivery in medicine. 2D materials are divided into ten major groups, including carbon-based 2D materials (includes graphene, graphene oxide, reduced graphene oxide, graphane, fluorographene, graphyne, graphdiyne, graphone), hexagonal boron nitride (hBN), graphitic C3N4, elemental 2D materials (elements groups 14 and 15), transition metal dichalcogenides (TMDs), transition metal oxides (TMOs), MXenes, 2D perovskite materials, 2D metal materials, and 2D clay materials (silicate clays and layered double hydroxides (LDHs)). In this paper, after the classification of these materials, the introduction, application, and related properties are investigated. So far, more studies have been done on graphene than other 2D materials. These materials are expected to have a similar capacity to graphene in terms of properties and applications, while ongoing research will increase the diversities of this category and depth of knowledge on these groups of materials.