Business websites are professional websites that are build purely for business reasons. They generally belong to organizations.
Their tasks include,
Providing company information
Providing company's products information
Marketing company's products
Providing help and support to costumers.
Selling company's products online.
BLOG
A blog is a frequently updated online personal journal or diary. It is a place to express yourself to the world. A place to share your thoughts and your passions. Really, it’s anything you want it to be. For our purposes we’ll say that a blog is your own website that you are going to update on an ongoing basis. Blog is a short form for the word weblog and the two words are used interchangeably.
Portal
Web portal is a specially designed website that often serves as the single point of access for information. It can also be considered a library of personalized and categorized content. A web portal helps in search navigation, personalization, notification and information integration, and often provides features like task management, collaboration, and business intelligence and application integration.
Web portals are also known simply as portals.
Wiki
A wiki is a Web site that allows users to add and update content on the site using their own Web browser. This is made possible by Wiki software that runs on the Web server. Wikis end up being created mainly by a collaborative effort of the site visitors. A great example of a large wiki is the Wikipedia, a free encyclopedia in many languages that anyone can edit. The term "wiki" comes from the Hawaiian phrase, "wiki wiki," which means "super fast." I guess if you have thousands of users adding content to a Web site on a regular basis, the site could grow "super fast."
Social online network
Social online network as "A website that provides a virtual community for people interested in a particular subject or just to 'hang out' together." While this is an accurate description, a more detailed definition of online social networking would also encompass all of the ways people can connect.
Online networks such as Facebook, Twitter, MySpace, and LinkedIn all offer users a variety of ways to increase their networks, share notes and various types of media, and connect on a variety of levels.