Depending on the definition of our boundary, systems can be characterized in several ways.
An open system is one where both mass and energy may cross the boundaries of the systems. Examples: pipes, turbines
A closed system is one where only energy may cross the boundaries (that is, mass cannot cross the boundary). Examples: an oven, this classroom
An isolated system is one which does not allow mass or energy to cross its boundaries.
Define open system, closed system, and isolated system