Legal drinking age. The legal drinking age is the age at which a person can legally consume or purchase alcoholic beverages. These laws cover a wide range of issues and behaviors, addressing when and where alcohol can be consumed.
An open system is a system that has external interactions. Such interactions can take the form of information, energy, or material transfers into or out of the system boundary, depending on the discipline which defines the concept.
A system may also be a closed system or an open system, depending on the relation between it and its environment. It is closed if matter cannot pass through its boundaries and it can exchange only energy with its surroundings. It is open if both matter and energy can pass through its boundaries.