Web applications are software that are designed to be used on the web using a user agent such as a browser.
A collection of files, grouped under a specific domain name and published on the Internet.
This web site (www.web-companies.com), for example, is a collection of HTML documents and images grouped under the www.webdesigndictionary.com domain name.
Web sites can be interactive in the sense that users are allowed to contribute to the content on the site, for example YouTube.com where users may upload videos.
Working according to the guidelines set up by search engines. Refers to good practices, versus black hat which refers to bad practices.
Wikis are informative pages about a particular topic or subject. Wikis can generally be edited even though some wikis are password protected to control contribution. The most famous wiki is Wikipedia.
WordPress is a CMS mainly used by bloggers.