This document defines different types of systems and their interactions with surroundings in thermodynamics. An open system can exchange both matter and energy with surroundings, a closed system can only exchange energy, and an isolated system cannot exchange either. Exothermic processes release heat to surroundings while endothermic processes absorb heat from surroundings. Vaporization and melting of substances are endothermic since they require energy, while freezing is exothermic as it releases energy.