Abstract: This paper addresses the need to define and discuss the relationship between the digital human model, the human digital twin and the digital twin. Nowadays, in scientific literature, the new terms human digital twin or digital twin are mentioned in different fields of applications, omitting the concept digital human model. However, a model is not the same as a twin. Simultaneously, the question of whether a digital human model can be a digital twin and what the relationships are between a digital twin and vice versa arises. Or how do the terms virtual humans, human digital twins, and digital human models interact? Is there a distinction between virtual and digital human models? All these questions are discussed and evaluated in this critical appraisal based on scientific literature research.