What is a System?

https://i.ytimg.com/vi/b3vHLUTzpc0/hqdefault.jpg?sqp=-oaymwE2CPYBEIoBSFXyq4qpAygIARUAAIhCGAFwAcABBvABAfgB_gmAAtAFigIMCAAQARh_IFkoLDAP&rs=AOn4CLBmn9Ea0X5EJK86j_mi0Xu6IpOUJw