An ideal language user a speaker/listener that is a member of a homogeneous speech community

Speech community

Speech community is a group of people who share a set of norms and expectations regarding the use of language. Speech communities can be members of a profession with a specialized jargon, distinct social groups like high school students or hip hop fans , or even tight-knit groups like families and...

, knows the language perfectly, and is not affected by memory limitations or distractions. Such a speaker/listener does not exist in the real world. The ideal language user is a subject of most linguistic theories because linguist can only study an idealized version of a language (I-language) because in the real world people make performance mistakes while speaking. The term was coined by Noam Chomsky

Noam Chomsky

Avram Noam Chomsky is an American linguist, philosopher, cognitive scientist, and activist. He is an Institute Professor and Professor in the Department of Linguistics & Philosophy at MIT, where he has worked for over 50 years. Chomsky has been described as the "father of modern linguistics" and...

.

http://www.articlearchives.com/humanities-social-science/language-languages-foreign/350145-1.html