domaindo·main /dəˈmeɪn, dəʊ-də-, doʊ-/ noun [countableC]1an area of activity, interest, or knowledgethe scientific domain.
2somebody’s/something’s domainCOMMERCE an activity controlled by one person, organization, industry etcMarketing treasury bills had been the exclusive domain of banks (=only banks could do it).
3PROPERTYan area of land or property owned and controlled by one person or organizationMr Li now controls a vast domain of container terminals, supermarkets and power plants.
4the public domain if information or property is in the public domain, it is available for everyone to use and not kept secret, or not kept as the property of a particular person or organizationThe matter is now in the public domain as a consequence of someone from his Department leaking information to the press.
A change in the law extended copyright protection to many books that otherwise would have entered the public domain (=become available for anyone to publish).