WordPress is an open source content management system running on PHP and MySQL often used as a blog engine. There is a WordPress StackExchange at http://wordpress.stackexchange.com/: if your question is related to WordPress but not webmastery, then your should ask it over there.
WordPress has a very active community and thousands of plugins and themes that can be downloaded from wordpress.org.
- Website: https://wordpress.org/
- Wikipedia: https://en.wikipedia.org/wiki/WordPress
- WordPress.SE: https://wordpress.stackexchange.com/