Microsoft has had a bit of a time naming the apps that users download from the Windows Store. First, they were being referred to Metro apps, though they had to stop the Metro naming after someone threatened to sue them over its use. Yesterday, Microsoft referred to the apps as "Windows 8 Store Applications."
Microsoft has now recanted that description and instead directed everyone to refer to the apps as "Windows Store apps." It's a bit shorter and easier to say and much more likely to catch on, though most people will probably still just refer to the Windows Store apps as "apps" due to the ubiquitous that term has come to be.