WHOIS is a complex topic, as this book explains, but the simplest explanation is that it is a record system for network resources, mostly, but not exclusively on the Internet. WHOIS is one of the most critical and controversial services on the Internet, yet there has been little or no comprehensive documentation. A WHOIS service can be queried to return a WHOIS record, which details who owns or manages an Internet resource. While this service may seem ordinary, WHOIS is one of the most debated issues in Internet policy. In theory, WHOIS is supposed to simply retrieve contact information; in practice, WHOIS varies widely in composition, access, and use. This text covers the universe of topics and issues including the 40-year evolution of the service, policy changes, comprehensive use instructions, service deployment, and advanced coding for programmers. The text is wide in its breadth and attempts to be somewhat deep in each of the major areas, but there are limitations to coverage in a single text.
Unlike computer programming, networking, or hardware development, WHOIS is a disconnected and esoteric discipline. It has many self-taught adepts as well as almost cultish followers. WHOIS is a deep and wide subject without dedicated texts or classroom instruction, a truly strange and hidden world. Welcome, you are about to become a WHOIS sorcerer.
From RFC11771 FYI on Questions and Answers to Commonly asked “New Internet User” Questions (1990)