A vanity wiki is a wiki used as a personal vanity press for advertising (including self-promotion), self-deprecation, or attempts to become an internet celebrity. A vanity wiki can sometimes be a bliki used for journaling, propagation of one's ideas and opinions, etc.
The term is by all means a POV because it is more about the believed intentions of the person or persons behind the endeavour and not about observable facts. So when anybody calls a wiki names, you know now what it means in this case.
See also Vanity wiki for the Wiki with the same name.