A Vlog is a blog that contains video. People who use video to tell their story or just share random thoughts are called "vloggers." The first videos released by lonelygirl15 on YouTube, Paytotheorderofofof vs. Dinosaur, YouTubers Secret Language, and First Blog / Dorkiness Prevails made many references to popular vloggers at the time, like thewinekone and paytotheorderofofof2.
Many of the most popular YouTube users are vloggers, as opposed to film-makers who distribute their videos on YouTube. Lonelygirl15 was supposed to appear, at first glance, to be just another vlogger on YouTube. By posting her videos as responses to other popular vloggers, Bree quickly developed a large audience, as fans of other vlogs watched her earliest videos.
See also entry on the vlogging influences of Lonelygirl15.