Those who blog, bloggers, carry out the activity of blogging, setting up a blog site, with a unique web address in order to do so. It's an abbreviation of 'web log'; a phrase that was first used in 1997, both as a noun and as a verb, a web log.
It's essentially a content management system, a way of getting content on to a webpage; it's a genre, a bit like diary writing, or bulletin posting. I mean, people add their posts or diary entries, with some regularity, if you're a blogger you do it daily at least, often several times a day.