The Dungeons and Dragons 4th Edition "system" is the common term used by gamers for the latest iteration of the d20 system.
Although Wizards of the Coast still puts a d20 logo (different from all the 3.x books - this one is squat and yellow), the system isn't usually referred to as d20 on the Wizards website. They tend to use the term "4e Game System" and have produced a license called the GSL 4e - Gaming System License 4th Edition. The WotC website also makes reference to a "d20 GSL" for non-fantasy based games.
Until we have better classification as to what this system is called, we are using this system to describe:
The core system used by Dungeons & Dragons 4th Edition
The core system used by third party products that are compatible with D&D 4th Edition.
If and when Wizards formally breaks off "d20 GSL" for non-fantasy based games, we will add that as a system and remove associated references (in the form of alternate names) to the "d20 GSL" here.