In thermodynamics, a process is a change in a system defined by an initial state, a final state, and the path followed. [1] A process, to note, must not be mistaken for a transformation, which is defined by only its initial state and final state. Said another way, a process, in thermodynamics, is defined as a method of operation in which specific quantities of heat and various types of mass and work are transferred across itsa boundary to and from the system to alter its state. [2]

References
1. Perrot, Pierre. (1998). A to Z of Thermodynamics, Oxford: Oxford University Press.
2. Mansoori, G. Ali. (2005). Principles of Nanotechnology: Molecular-based Study of Condensed Matter in Small Systems, (chapter 3: “Thermodynamics and Statistical Mechanics of Small Systems”, pgs. 84-114 [88]). World Scientific.