Learner's definition of DOMAIN
1 : the land that a ruler or a government controls : territory 2 : an area of knowledge or activity
— often + of
My sister is the math expert in the family, but literature is my domain.
Childcare is no longer solely a female domain.
3 a : a section of the Internet that is made up of computers or sites that are related in some way (such as by use or source) b : domain name
◊ An abbreviation of an Internet site's domain (such as .gov, .org, and .com) is included in its address: www.Merriam-Webster.com.