A Blog is a nickname for a weblog. A weblog is a frequently updated online journal. It can have a single author or a group of authors. Blog sites are usually focused in topic, but it is certainly not a requirement.
When combined with feeds, blogging is an easy way for an individual to publish content in a quick and efficient method. Since users can subscribe to a feed, an individual can "push" updates to the user, without any action on the end user's part.