In comics vocabulary, a splash page is simply a full page of art. Often used on the first page to draw the reader in, the splash usually contains the title and credits. It also serves to establish the setting, time, and even the primary characters of the story.
Splash pages that aren't on the first page are called interior splashes. These pages may include titles and credits; that is your call. An interior panel that is bigger than the others is called a splash panel. Splashes shouldn't be overused. If there isn't a good reason to have them, such as a plot point that must be made or a fantastic visual waiting to be portrayed, just skip them. They should always be reserved for dramatic or momentous visuals.
Because larger panels serve to break up the monotony of pages divided into multi-panel spreads, they have great visual impact and usually portray a moment of importance and drama in the story. Done well, they vary the predictable rhythm of the page and help hold the reader's interest.
SPLASH PAGES ARE USED LESS THESE DAYS IN REGULAR COMICS BECAUSE SPACE IS AT A PREMIUM WHEN YOU HAVE TWENTY-TWO PAGES TO TELL A STORY. HOWEVER, THEY ARE APPROPRIATE AND NOT AN INDULGENCE WHEN USED IN GRAPHIC NOVELS WHERE THANKS TO THE HIGHER PAGE COUNT YOU HAVE THE LUXURY OF TELLING MORE OF THE STORY.