Wiki is a page/site where the end-user can interact with the rendered page, change few settings, edit contents and so on. Now Google has come up with something called Search Wiki, where you can re-order or re-arrange your search results which helps Google to know your preference and priority. This info about your preference is used by the company to render you better personalized search results and the my guess is that the system would keep performing better as we interact more & more with the rendered results. You need to be logged in though to use the system.
Microsoft on the other hand has already a research prototype “U RANK” which works in the similar way, you can re-arrange, move up, re-order your rendered search results. You need to be logged in though.