A closed system in thermodynamics is one that can transfer:

1. The system is the matter and its environment relevant to a particular case of energy transfer. 2. Everything outside of that system is called the surroundings. 3. A closed system is one that can transfer energy but not matter to its surroundings. 4. A stovetop system is open by contrast, because heat can be lost into the air. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 6 'Metabolism', sections 6.1-6.5_