WordPress is the most easy to use website and blog creation tool and content management system (or CMS) available.
A content management system is a computer application that supports the creation and modification of digital content. It typically supports multiple users in a collaborative environment.
WordPress is an online, open source website creation tool written in PHP. But in non-geek speak, it's probably the easiest and most powerful blogging and website content management system (or CMS) in existence today.
WordPress started in 2003 with a single bit of code to enhance the typography of everyday writing and with fewer users than you can count on your fingers and toes. Since then it has grown to be the largest self-hosted blogging tool in the world, used on millions of sites and seen by tens of millions of people every day.
WordPress started as just a blogging system, but has evolved to be used as full content management system and so much more through the thousands of plugins and widgets and themes, WordPress is limited only by your imagination. (And tech chops.)