Learner's definition of DOMAIN
an area of knowledge or activity
My sister is the math expert in the family, but literature is my domain.
Childcare is no longer solely a female domain.
— often + of
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)
◊ An abbreviation of an Internet site's domain (such as .gov, .org, and .com) is included in its address: www.Merriam-Webster.com.