Avatar: An avatar online is a symbol or picture that marks your comments or presence--usually thumbnail size, and not a remarkable part of your interactions.  (see game definition for more about game avatars)

Blog: Originally "web log", a blog is usually a personal or business site that keeps track of what's going on personally or professionally.  You can think of it as a diary or journal that's open to the public and allows comments by readers.

Creative Commons:  Creative Commons is non-profit company that provides copyrights to creators that are somewhat customizable by the creator.  It's generally less restricting than traditional copyrights while not completely open-source.

Cyber: A prefix refering to places, activities, and interactions on-line.

Cyberspace - Cyberspace is a term coined by writer William Gibson (and popularized in his cyberpunk classic Neuromancer) and catapulted into even more popular usage by Neil Stephenson (in Snowcrash). What was a science fiction concept when Gibson coined the term has come to mean the internet based on remarkable similarities between the fictive vision and the actual resource we use today.

FaceBook: FaceBook is a popular social networking site that is geared towards students and young professionals, designed to keep friends in touch.

File sharing: Beyond the obvious (sharing files between people and computers), file sharing is often known as peer-to-peer (also P2P) sharing, and lets multiple people acquire a file at the same time by distributing the work load among multiple computers and network connections.

Forum: A forum is an online (and usually text-based) space for people with a mutual topic of interest to argue, exchange information, and share opinions.

Group-sourcing:  Also called "crowd sourcing", group-sourcing refers to soliciting or allowing people to co-create or fix a project together.  Both open-source software communities and wikis are examples of this.

IM (instant message): One way to think about instant-messaging is as a space that lets you e-mail back and forth quickly in a text-based conversational style.

MySpace: MySpace is a popular social networking site that allows people to create and customize pages, post music, videos, and artwork, and keep in touch with friends or fans.

Open-source:  Open-source software is designed, modified, and distributed for free by voluntary groups, with the caveat that if you improve upon the software, you re-distribute it to the group in order to improve the community's work as a whole.

Second Life: Second Life is a virtual world created by Linden Labs that users design content for and interactions within.  It's not a game but is a common 3D space for people to interact via avatars.

Social Networking Website: There are a variety of types, but generally they're online communities that are designed for meeting or keeping in touch with people (Facebook and Myspace are popular examples).

Vlog: A vlog was originally "video log", and it is much like a blog but with an emphasis on videos.

WebQuest: A webquest uses the internet and the information it contains as a game space, and quests are designed to be accomplished by finding certain types of information (originally used in an educational context). For more information on webquests and how to make them, check out webquest.org.

Web 2.0: Web 2.0 is a name given to the recent trend to leverage the power of the internet to increase collaboration, information-sharing, and networking.  Social networking sites, blogs, vlogs, and wikis are considered part of Web 2.0, and although the tools to create such sites have always been part of the web, they're just now becoming a truly notable part of it.

Wiki: A wiki is an online information source that is added to and edited by anyone that uses the wiki and wants to contribute.

YouTube: YouTube is a popular video site where people can upload videos they've created or copied for others to see and comment on.