From the Wikipedia page on WHOIS:
WHOIS (pronounced as the phrase who is) is a query/response protocol that is widely used for querying databases in order to determine the registrar or assignee of an Internet resource (such as a domain name, an IP address block, or an autonomous system number).
The WHOIS system originated as a method for system administrators to obtain contact information for IP address assignments or domain name administrators. The use of the data in the WHOIS system has evolved into a variety of uses, including:
- Supporting the security and stability of the Internet by providing contact points for network operators and administrators, including ISPs, and certified computer incident response teams;
- Determining the registration status of domain names;
- Assisting law enforcement authorities in investigations for enforcing national and international laws, including, for example, countering terrorism-related criminal offences and in supporting international cooperation procedures. In some countries, specialized non-governmental entities may be involved in this work;
- Assisting in the combating against abusive uses of Information communication technology, such as illegal and other acts motivated by racism, racial discrimination, xenophobia, and related intolerance, hatred, violence, all forms of child abuse, including pedophilia and child pornography, the trafficking in, and exploitation of, human beings.
- Facilitating inquiries and subsequent steps to conduct trademark clearances and to help counter intellectual property infringement, misuse and theft in accordance with applicable national laws and international treaties;
- Contributing to user confidence in the Internet as a reliable and efficient means of information and communication and as an important tool for promoting digital inclusion, e-commerce and other legitimate uses by helping users identify persons or entities responsible for content and services online; and
- Assisting businesses, other organizations and users in combating fraud, complying with relevant laws and safeguarding the interests of the public.