A blog, or weblog, is an online journal, diary, or serial published by a person or group of people.

Blogs are typically used by individuals or peer groups, but are occasionally used by companies or organizations as well. In the corporate arena, the only adopters of the blog format so far have tended to be design firms, web media companies, and other "bleeding edge" tech firms.

Blogs often contain public as well as private content. Depending on the functionality of the CMS software that is used, some authors may restrict access — through the use of accounts or passwords — to content that is too personal to be published publicly.

Reference http://codex.wordpress.org/Glossary