What is a domian ?

From my perspective a Domian is in general, a domain is an area of control or a sphere of knowledge.

A list of domian would be
.net : Networks
.org : Organisations
.edu : Educational
.gov : US Government
.int : International Organisations
.mil : US Dept of Defense

Org .Net
1.cars.org 1. Topklass.net
2.houses.org 2.G-unit.net
3.commercebank.org 3.spamcot.net

Edu- Gov
1. Lasalle.edu 1.cia.gov
2.princeton.edu 2.in.gov
3.harvard.edu 3.nasa

INT MIL
1.who.int 1.Nic.Mil
2.wipo.int 2.Navy.Mil
3.unfcc.int 3.dtic.mil

What can a internet user determine about an organization from it web address?

A internet user can determine what would the web site is based on or if the web site is selling things on the page.