<h3>Closed System Definition</h3><p>A closed system is a type of <a href="https://www.thoughtco.com/thermodynamics-definition-602127" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">thermodynamic</a> system where <a href="https://www.thoughtco.com/definition-of-mass-604563" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">mass</a> is conserved within the boundaries of the system, but <a href="https://www.thoughtco.com/definition-of-energy-in-chemistry-604456" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="3">energy</a> is allowed to freely enter or exit the system.</p>