Definitions
A concept is an abstract term that is semantically defined by its association or usage with other terms that are not directly observable (Van de Ven 2007, p. 113). A construct is a middle-range term that references constitutive components of a concept, but the component parts are not directly observable (Van de Ven 2007, p. 113).
An example
Consider the social structure of an organization (Van de Ven 2007, p. 114). As a concept, an organization’s social structure is defined as the formal configuration of roles and authority relationships existing among participants within an organization. As a construct, an organization’s social structure is analytically separated into three components of authority relationships among roles: (1) centralization of decision making authority; (2) formalization of rules, policies, and procedures; and (3) complexity, or the number and interdependence of role relationships.
Reference
Van de Ven, A. H. (2007). Engaged scholarship: A guide for organizational and social research. Oxford University Press on Demand.