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.
OpenStack is essentially a cloud operating system. You can think of it as an Operating System for running and managing a huge number of Operating Systems (like windows,linux,etc). And most importantly, it is OpenSource. (unlike the popular Amazon AWS)