When you aren't ready to build a full website, but your company or organization needs to start to have an internet presence, it can make a lot of sense to post a single page website that can go up quickly and without hassle. There is no sitemap, no navigation, and very little content required. The benefit is that you have somewhere to point people, and you start to get on the radar of search engines before building your full site.
Other people in the industry may refer to this as a splash site, a one-pager or a micro-site, although to us a micro-site will have up to ten pages of navigable content.
When creating a splash page, we think it is important to still take a professional and thoughtful approach, so that the effort does not degrade your company or organization in the eyes of visitors. This counts out the animated gif with the shoveling construction worker and "website coming soon." Please don't go there.