Web 2.0 is the second generation of web-based communities and hosted services - such as social-networking sites, weblogs, wikis, and collaborative tagging (folksonomies) - tending to facilitate creativity, collaboration, and sharing information between users.
In order to use Web 2.0 applications or services, the internet user only needs to employ a web browser, no proprietary software is necessary.

Description of some essential terms and technologies

Weblog A blog or weblog is a website where entries are published frequently in reverse chronological order. The content of a weblog can be text, audio, video, photography or the combination of these media formats. At the end of 2007 more than 112 million blogs were counted by the blog search engine Technorati.

Wiki A wiki is (social) software that facilitates internet users to create, edit or link webpages. As a form of knowledge management wikis are employed as a collaborative webtool. Many wikis are open to being altered and updated by the general public without requiring them to register a user account. The world's biggest wiki is wikipedia.org, a multilingual, web-based, free content encyclopedia project.

Podcast Podcast or podcasting is a way of distributing a collection of digital media files such as audio or video. Podcast is a morphene which fuses the terms Pod (Portable on demand) and broadcast. Podcasting is different from other digital audio and video delivery in the use of syndication feed enclosures. This allows podcasts to be automatically downloaded to a user's media playback device. The author or producer of a podcast is called podcaster.

RSS RSS stands for Really Simple Syndication (or Rich Site Summary) and is a structured data format for publishing or collecting frequently updated content from weblogs, podcasts or news headlines. The document itself is often called web feed or RSS feed and contains a summary from the correspdonding website. RSS might be considered as the core piece for internet data exchange and syndication in web 2.0. It makes it possible for users to keep up with their favorite web sites in an automated manner instead of checking them manually.

Folksonomies Social bookmarking, social and collaborative tagging or social indexing are measures of collaboratively creating and managing tags to annotate a certain web content. These methods are user-driven and -generated. With the help of folksonomic tagging any content can be categorized with keywords. Thus folksonomies offer an easy access to search, discover, and navigate information. Social tagging and indexing is implemented on this platforms: del.icio.us, digg, furl, simpy or flickr (amongst others).

Social networks and services Social networks connect people on a low cost level and makes it easy to develop and built upon social ties based on similar activities or interests. Social networking is the basic principle of the Internet and is nowadays established in online communities / platforms like Facebook, Bebo, MySpace or Last.FM. Each user is able to interact with friends or colleagues in multiple manners: chat, messaging, email, video, voice chat, skype, file sharing, blogging, discussion groups, etc.

Some of the descriptions above are taken from the free encyclopedia Wikipedia. A more detailed introduction of the term Web 2.0 (and it's technologies) can be found there.