An internet site is a normal site that anyone on the internet can access (e.g., www.msn.com, www.microsoft.com, etc.). You can set up a site for your company that can be accessed by anyone without any user name and password. The internet is used for public presence and a primary marketing tool managed typically by web programmers and a system administrator.
An intranet (or internal network), though hosted on a Web site, can only be accessed by people who are members of a specific network. They need to have a login and password that was assigned to them when they were added to the site by the site administrator. The intranet is commonly used as an internal tool for giving employees access to company information. Content is driven by business relevance, business rules and has increasingly become a common tool in larger organizations. An intranet is becoming more and more the preferred method for employees to interact with each other and the central departments in an organization, whether or not the organization has a Web presence.