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.
Open-loop systems. Open-loop systems are set up to achieve desired results, but there's no way of checking if the results have been achieved. For example, an old-fashioned heating system might include: 1  input: an on-off switch. 2  process: boiler (water heater) and pump. 3  output: radiator.