A blog (a portmanteau of web log) is a website where entries are commonly displayed in reverse chronological order. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.

Many blogs provide commentary or news on a particular subject; others function as more personal online diaries. A typical blog combines text, images, and links to other blogs, web pages, and other media related to its topic. The ability for readers to leave comments in an interactive format is an important part of many blogs. Most blogs are primarily textual, although some focus on art (artlog), photographs (photoblog), sketchblog, videos (vlog), music (MP3 blog), audio (podcasting) are part of a wider network of social media. Micro-blogging is another type of blogging which consists of blogs with very short posts.

As of December 2007, blog search engine Technorati was tracking more than 112 million blogs

To put it as simply as possible - a blog is a type of website that is usually arranged in chronological order from the most recent ‘post’ (or entry) at the top of the main page to the older entries towards the bottom.

Blogs are usually (but not always) written by one person and are updated pretty regularly. Blogs are often (but not always) written on a particular topic - there are blogs on virtually any topic you can think of. From photography, to spirituality, to recipes, to personal diaries to hobbies - blogging has as many applications and varieties as you can imagine. Whole blog communities have sprung up around some of these topics putting people into contact with each other in relationships where they can learn, share ideas, make friends with and even do business with people with similar interests from around the world.

Blogs usually have a few features that are useful to know about if you want to get the most out of them as a reader.