Short for World Wide Web Consortium. W3C's mission is to "lead the Web to its full potential" by developing Web standards. W3C consists of a staff of technical experts, members and invited experts from the public. The larger webmaster community also has a role to play in providing input on the standards developed by W3C.
The Wayback Machine (http://archive.org/) is a large archive of web pages, cached since 1997. In simple terms, the Wayback Machine takes "snapshots" of web pages. It uses a spider that finds pages by following links - similar to the spiders used by search engines. If your web page is well-linked from other pages, the Wayback Machine will find it. The Wayback Machine can be blocked from archiving your site through the use of a robots.txt file.
Web space usually refers to hosting space or server space allocated to a specific web site. Most web sites are hosted on shared servers where only a portion of the available space is allocated to each site.
Refers to good practices, versus black hat which refers to bad practices. In search engine optimization terms, white hat practices would refer to those optimization techniques that do not attempt to manipulate search results in an unfair or dishonest way.
The empty space between design elements on a web site, for example an unused bit of page between a horizontal menu and the body text of the web site. White space is used to separate design elements and create visual groupings of design elements.
Note that white space does not have to be white - the term refers to any area on the site where the background is visible through the content of the site.
WYSIWYG is short for "What You See Is What You Get". A WYSIWYG HTML editor allows the web designer to work on the web site without editing the code directly. The WYSIWYG editor has a user-friendly interface which allows the designer to place images, change attributes etc. without having to write the HTML markup. It is worth noting that most WYSIWYG editors are somewhat limited and that professional designers should have a good command of the language in order to be able to edit the code directly.