First introduced in 2009 (Players and Goalies), GVS (Goals Versus Salary) gradually snuck into the mainstream and NHL front offices, as covered in January 2012 by ESPN's Craig Custance.
GVS is simply Tom Awad's GVT with the salary cap hit taken into account. GVT, Goals Versus Threshold, is a player's contributions calculated against the threshold of a replacement-level player, like someone you'd call up from the AHL. GVS is instead calculated against the threshold of what you could get for the same salary cap hit.
GVS can be used on a team level to determine how well a team is managing its cap space, or it can be used at a player level to determine how well a particular player is earning their contract. For more information it is regularly used and explained over at Hockey Prospectus and Arctic Ice Hockey.
Since then it has been used in a number of ways, including my analysis of the Mike Fisher trade, Timo Seppa's analysis of free agent signings for ESPN, Phil Myrland's analysis of back-up goalies, Ryan Poplichak's look at team cap management, George Ays analysis of the New York Rangers, and even Neil Greenberg's analysis of Alexander Semin.
GVS statistics can be found in the NHL Super-Stats Sheets posted here annually, and the data for all seven seasons, including 2014-15, can be downloaded right here.