It is just a tool to help you to create blog. Similiar as blogger tool. WordPress is a blog publishing system written in PHP and backed by a MySQL database. Cheers!
Technically wordpress is for blogs, but its also easy to understand and code. So if you know even a little bit of html, you can probably set up a full site on it. (see my sig for an example if you wish, those sites are wordpress, but I've edited out most of the blog features.)
its a blogging software read more: www.wordpress.com www.wordpress.org http://en.wikipedia.org/wiki/WordPress
its is a CMS (Content Management System) it is mosly use for blogs and lots of text as it makes it easy to work with because it is made in php and MySQL it also has many mods that other people have made so it makes it even better. its also lets readers of the site join to add to comments ect just makes life easer for you the webmaster to get information to your users