In an exothermic process, the system releases heat that is absorbed by the surrounding; in an endothermic process, the system absorbs heat from the surrounding.
The diagrammatic representation of endo and exothermic reaction is attached for quick reference. From the diagram, it can be seen that during exothermic reaction, product formed is stable as compared to reactant, while in case of endothermic reaction reactant is more stable than product.
