Well splash page is a front page of a web-site that don’t provide the actual content, but offers visitors some kind of intuition or background information for what the site is about. Designers use splash pages in their portfolios to impress potential clients with eye-candy. Companies tend to make use of them to draw users’ attention to their latest products.
A splash screen is an image that appears while a game or program is loading. It may also be used to describe an introduction page on a website. Splash screens sometimes do not cover the entire screen, but only a rectangle near the center. The splash screens of operating systems and some applications that expect to be run full-screen usually cover the entire screen. (c) Detailed info look here
you have the best possible answer on splash page. It is basically meant for guiding users. For SEO it has nothing to do. If it increases your bounce rate then it's bad for site otherwise its ok.
On the Web, a splash screen or splash page is a page of a web site that is a sort of pre-home page front page.