A blog (a truncation of the expression weblog) is a discussion or informational site published on the World Wide Web consisting of discrete entries ("posts") typically displayed in reverse chronological order (the most recent post appears first). Until 2009, blogs were usually the work of a single individual, occasionally of a small group, and often covered a single subject. More recently, "multi-author blogs" (MABs) have developed, with posts written by large numbers of authors and professionally edited. MABs from newspapers, other media outlets, universities, think tanks, advocacy groups, and similar institutions account for an increasing quantity of blog traffic. The rise of Twitter and other "microblogging" systems helps integrate MABs and single-author blogs into societal newstreams. Blog can also be used as a verb, meaning to maintain or add content to a blog.

.blog is a proposed Generic top-level domain intended for use by blogs as the name suggests. In late 2013, due to concerns over "name collisions", wherein companies could potentially be using some proposed gTLDs internally for their own use, the ICANN halted progression of .blog and 24 other proposed gTLDs pending further review.