In physical science, an isolated system is either of the following: a physical system so far removed from other systems that it does not interact with them. Wikipedia

A system without any external exchange Wikipedia Disambiguation

Physical systems that don't interact with other parts of the universe Wikidata

A system that does not interact with its surroundings. Depending on context this may mean that its total energy and/or momentum stay constant. In thermodynamics, isolated is usually used to indicate that the system's energy does not change. In mechanics it is used to indicate that the system's momentum does not change. Wiktionary