The noun domain has 5 senses (first 2 from tagged texts)
1. (4) sphere, domain, area, orbit, field, arena -- (a particular environment or walk of life; "his social sphere is limited"; "it was a closed area of employment"; "he's out of my orbit")
2. (2) domain, demesne, land -- (territory over which rule or control is exercised; "his domain extended into Europe"; "he made it the law of the land")
3. domain -- (the set of values of the independent variable for which a function is defined)
4. world, domain -- (people in general; especially a distinctive group of people with some shared interest; "the Western world")
5. domain, region, realm -- (a knowledge domain that you are interested in or are communicating about; "it was a limited domain of discourse"; "here we enter the region of opinion"; "the realm of the occult")