This is a system in which there is no exchange of matter, energy and information with the external environment or environment. This distinguishes a closed system from an isolated system, where information exchange is allowed, and also from a closed system, where energy exchange is possible.
Give examples of closed systems. Universe, mathematical pendulum.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.