A domain is a specific area of knowledge or activity. In the context of the internet, a domain refers to a unique address that identifies a website, such as example.com. Each domain is part of a larger system called the Domain Name System (DNS), which translates user-friendly names into numerical IP addresses that computers use to communicate. In biology, a domain can also refer to a major category in the classification of life. The three primary domains are Bacteria, Archaea, and Eukarya. These domains group organisms based on fundamental differences in their cellular structure and genetics, helping scientists understand the diversity of life on Earth.