What are open and closed systems?
The concept of open and closed systems is commonly used in thermodynamics to describe the interactions between a system and its environment. A system can be thought of as the region or process of interest, while everything outside it is its environment. Systems can be extremely simple or very complex.
If a system is capable of exchanging matter and energy with its surroundings, it is known as an open system. We can think of our body as an open system. We eat food (matter intake), we excrete waste materials (matter lost to the environment) and we receive heat from the sun, among other sources (energy exchange).
On the other hand, if a system can only exchange energy with its environment, it is known as a closed system. One can think of Earth as a closed system, since it receives only energy from sunlight, while the overall matter exchange is extremely small (how much matter we get from space in the form of meteorites, etc.).
There are also isolated systems, which cannot exchange either matter or energy with the environment.
Hope this helps.