It’s the most common definition of the word, at least. As web publishing has evolved and gotten more diverse, it has become harder and harder to define exactly what a blog is. Many of the mainstream news sites display some of the content in a reverse chronological order, after all, and many sites that generally are classed as blogs – sites like Kotaku, TechCrunch and TMZ – have areas where the content is not presented in reverse chronological order. There’s no clear line where blogs end and news sites start. Mostly, it’s a “you know it when you see it” sort of thing.
As for the word itself, blog is an abbreviation of the word “weblog” – a combination of the word “web” and the word “log”. The word “weblog” was originally used by Jorn Barger, who posted frequent updates about his life and interests on the website “Robot Wisdom Weblog”. The shortened version of the word, “blog”, was first used by Peter Merholz who jokingly split the word “weblog” into “We blog” in the sidebar of his personal site. Not long after, developer and entrepreneur Evan Williams co-founded the blogging software Blogger, which helped popularize the term further.
WordPress was originally conceived as a management system for blogs. Over the years, it has been updated with features that makes it as viable as a CMS as it is as a blogging engine, but it’s still a popular choice for people who just want somewhere to jot down their thoughts every now and then. When you create a new WordPress installation, it will default to displaying the blog archive on your front page. You can change the front page to a static page in Settings → Reading, and when you do, you can select another page to use as the primary archive page for blog posts.