Noun
1. 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. territory over which rule or control is exercised;
"his domain extended into Europe""he made it the law of the land"3. the set of values of the independent variable for which a function is defined
4. people in general; especially a distinctive group of people with some shared interest;
"the Western world"5. 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"