A vlog is a video documentation of a person's life. This can be done regarding the experiences one has, similar to a diary or pertain to one's views on specific matters.
The terms can mean many things as it evolved over the years. For example, a vlog can be a specific video that a person makes. However, it also could mean one's channel. We often hear people say subscribe to my vlog. Also, like many things in the digital world, it also takes on the form of a verb such as "vlogging".
It essentially is the combining of the terms video and blog to reach vlog.