A term used to describe small 2-5 page web sites containing a highly focused sales message and call to action (order page). Mini sites are extremely fast and easy to build and provide a number of benefits including boosting cashflow quickly, creating a network of interrelated sites (common theme) that the search engines will rank high, etc.
There are 2 specific marketers who I feel know the most about mini sites and how to use them effectively to make a significant income online:
Phil Wiley
Marlon Sanders
These guys are experts with mini sites.