a regularly updated website or web page, typically one run by an individual or small group, that is written in an informal or conversational style.
A blog is basically a website on which time relevant content are published by site owners and writers. The content is mostly indexed reverse chronologically, i.e., newest updates coming on top and older ones later.
The content published on a blog are called blogposts or simply posts. The writers writing on a blog are best known as bloggers.
The word blog is the short language form of ‘weblog’. As logs are indexed by time, blogs maintain the same theory.