More about PCI compliance can be found here on the PCI Security Standards Council website:
PCI Security...We serve those who work with and are associated with payment cards. This includes: merchants of all sizes, financial institutions, point-of-sale vendors, and hardware and software developers who create and operate the global infrastructure for processing payments...
The Council was founded in 2006 by American Express, Discover, JCB International, MasterCard and Visa Inc. They share equally in governance and execution of the Council's work...
You also need to have your web hosting compliant if any information is stored online.
Those who have gone through the process of becoming PCI compliant are welcome to give input/comments about the whole process.