A Wiki site is basically a user-generated information site. The most famous example of a wiki site is wikipedia.org. Check out this link: http://en.wikipedia.org/wiki/Wiki That is a wiki page on wikipedia.org explaining exactly what a wiki is
Consequently, even though the content on Blogspot and Wordpress blogs is generated by numerous users all over the world, they cannot be considered wiki pages because one cannot edit or update a post that was written by another user. There are exceptions of course, but generally, this is why these are not wiki.
A wiki is a website that allows the easy creation and editing of any number of interlinked web pages via a web browser using a simplified markup language or a WYSIWYG text editor. A web page that is part of a WIKI system, that has the characteristic of being editable by any browser and its content can therefore be changed by the web users is called as WIKI Page.