An open system is a system in which both heat and mass are escaping/coming in. (Think of a glass of water; water is evaporating and heat is melting the ice). A closed system is when only heat is escaping/coming in (A bottle of water where water vapor can't escape, but it can still be warmed) An isolated system occurs when neither heat nor mass can escape/come in (Think of a thermos; neither heat nor vapor can escape). Hope this helps!