A Rogue (also known as FraudTool) is a standalone malware computer program that pretends to be a well-known program, or a non-malicious one (such as an Antivirus), in order to steal money and/or confidential data. It is often the case in which these malware have also, inside them, adware functionality.
A Rogue-AV (also known as FakeAV) is a Rogue that fakes to be an Antivirus solution which, once installed on a user's computer, pretends to find one or more computer viruses and/or malware. Obviously, the Rogue-Antivirus does not perform a real scan, and then the computer can be absolutely clean. Once it has reported the presence of these hypothetical malware, the Rogue-AV usually proposes for the user to buy a theoretical paid version to clean the computer. Obviously, there is no paid version, and once users provide their credit card data and complete the transaction, they do not have access to any paid version.