WikiData is the project to take the game data shared by the developers and make it available on the wiki. The goal is to have data pages which are not normally edited by users, and thus can be overwritten when changes are made. These data pages will be stored in Template pages with names like "WikiData/TableName/PageName" so that they can be called passing in a Formatting Template to send the actual data to. This will allow us to send the same data to different Formatting Templates under different circumstances.
TableName tells us which named Parameters we can expect in the pages beneath. For example, "WikiData/Roles" lets us know that everything in that page or in a page that starts with "WikiData/Roles/" will all contain named Parameters "Role" and "SortKey". As the development of these structures stabilizes, they will be documented here, and the source code for the .NET project that reads the Developer Spreadsheets and writes the Wiki Pages will be put up on SourceForge or a similar platform.
Normally, it's a good idea to avoid storing the same data in two places, but because of the special considerations for making the wiki work, there will likely be several places where the same data is repeated. For example, "WikiData/Feats/Cantrips" will contain all the Cantrips data, and each Cantrip will also be listed under its own name such as "WikiData/Feats/Blinding Pattern".