Vanity page
A vanity page is a page that a person posts for promotion of himself, his company, his ideas, etc. Essentially he uses the wiki as a free Template:W. A page whose content is off-topic is particularly susceptible to being viewed as a vanity page. Mainspace content is also often more closely regulated than userspace.
Such pages are sometimes deleted as spam, but norms differ from one wiki to another. Wikipedia clearly Template:W that it is not a free web host and that vanity content will therefore be deleted. For one thing, vanity pages are deemed to manifest a conflict of interest. Other sites are willing to be more Facebooky and to welcome vanity pages as potentially useful user-generated content, so long as there is an actual human being who has taken enough interest in that particular wiki to post his content, rather than a bot advertising generic erectile dysfunction remedies. The idea may be that the user has an incentive to cross-promote the wiki as a way of drawing further attention to his content.