 A digital twin, DT, is a virtual representation of a physical object which is connected to its physical counterpart through data exchange. It is used to monitor, plan, optimize, maintain, and remotely access complex industrial systems. DTs have been gaining popularity with the advent of industry 4.0, leading to increased confusion among researchers and practitioners regarding the various types of DTs and their definitions. This paper provides a comprehensive review of the existing literature to clarify the differences between the various types of DTs and their definitions. Additionally, this paper discusses the potential benefits and drawbacks of using DTs in order to help researchers and practitioners make informed decisions about whether or not to use them. This article was authored by Moultrie Singh, Everett Fuhinmayer, Owen P. Hinchie, and others.