This article aims to establish and summarize the scientific approaches related to the concept of stress. Beyond this popular conception, however, there is wide disagreement over a more exact definition and over how stress should be measured. This article provides an overview of the literature regarding the definition of stress. This article highlights and explains some theoretical models (as the cognitive activation stress theory). The novelty of this article consists in combining the definitions, the conceptual and explanatory models of stress and providing new ways to explain this psychological concept.