Noun:
1: field, orbit, arena, domain, area, sphere 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: 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"