A system is simply something that a person or a scientist or researcher wants to study. It's the object of interest, okay? And the object could be as simple as the eraser. It could be this marker, it could be this whiteboard, it could be me, it could be the room, the building, this system. For example, if we chose this eraser to be the system has certain properties, it has a certain weight, it has a certain mass, it has a certain volume, certain density, certain pressure, certain height, length and width. It has certain properties that are used to quantify this system.