While your particular example is a bit overblown and extreme, I think you're referring to what is known as Splash Page (or Splash Screen).
Splash screens are typically used by particularly large applications
to notify the user that the program is in the process of loading. They
provide feedback that a lengthy process is underway. Occasionally, a
progress bar within the splash screen indicates the loading progress.
A splash screen disappears when the application's main window appears.
Splash screens typically serve to enhance the look and feel of an
application or web site, hence they are often visually appealing. They
may also have animations, graphics, and sound.
The Java programming language has a specific class for creating splash
screens, called java.awt.SplashScreen  that handles standard splash
screen functions, e.g. display an image centered on screen then
disappears when the first program window opens.
On the Web, a splash screen is a page of a web site that acts as a
front page prior to displaying the home page. Designers may use splash
- to direct users to the appropriate website for their country or language preference
- to direct users to a low-bandwidth site or one more accessible to disabled users
- as an additional form of advertising
- to restrict access to content such as pornography, alcohol advertising or sales, or gambling
- as an aesthetic complement to the main page
- To grab someone's attention to take them to a page with more details usually for a product that they are selling.