A blog is web site for a specific person or a specific group to post articles and visitors can comment on them. In a blog the control of content and value is driven by a single person or small group. A discussion board is used to solicit feedback from others by generating dialogue. Anyone can post a message and users can respond to each other. On a discussion board control of content and value is shared equally across all users.
According to Wikipedia, the world’s largest wiki site:
A Wiki ([ˈwiː.kiː]or [ˈwɪ.kiː]) is a type of website that allows users to add, remove, or otherwise edit and change most content very quickly and easily.
Wiki technology was originally designed for online collaboration among loosely affiliated software developers. Now wikis are comprised of community members who are passionate about subjects ranging from business, education, video games and movies to food, fashion, personal development, and environmental sustainability. Other examples include companies that use wikis for collaborative knowledge building, to solve problems remotely, and to organize and manage projects through connection with geographically dispersed employees.
The name “Wiki” was inspired by the Hawaiian word wiki or wiki-wiki, meaning “quick”. In 1995 Ward Cunningham, an American developed the first wiki. He remembered the wiki-wiki shuttle buses that run between terminals at Honolulu International Airport and as he wanted an alternate word for “quick” for his product that would allow for quick, collaborative editing so he chose “wiki”.
Wikis in Plain English
Wetpaint Wikis in Plain English
Free wikis are available on the internet where you can create your own wiki web projects in minutes. Many wiki farm companies generate revenue through the insertion of advertisements, but often allow payment of a monthly fee as an alternative to accepting ads.
Wikis are based on the idea that the crowd, collectively, has a greater sum of knowledge than just one individual. That means collaborating with others is the key to creating a successful wiki. Collaboration means you work together to build, design and make decisions on a wiki. No one person owns or rules a wiki. Rather, it is built, supported and owned by all participating community members. — Wikia Community Guidelines
A wiki needs to be about something to be successful. It needs to appeal to a niche that isn’t entirely satisfied elsewhere and its main purpose is to share information. The important rule of thumb is to establish and understand the goals for your wiki early on and implement it accordingly. — Wiki Best Practices