A splash page or often also known as a landing page is a page that a user first lands on with the option to then proceed to the main website. These pages are used for a number of reason such as promoting a particular product or service.
The advantages of creating a splash page allow you to tailor the design and content of the page to be very specific to the product or service you are creating. It also makes it easier to optimise for the search engines.
If you use Google Adwords, you can create landing pages for your ads that are highly relevant to your Google Adwords ad group content. This will not only give the user a better experience but also allow you to improve your quality score which will in turn reduce the cost that you pay per click on your keywords or your ad groups.