PCI DSS stands for Payment Card Industry Data Security Standard and contains a set of rules for secure processing credit card transactions. In principle, all those involved in a credit card payment (e.g. merchants and PSPs) are subject to these rules as soon as they process, transfer or save credit card data.

There are 12 basic requirements defined by PCI DSS Standard: 

1. Install and maintain a firewall configuration to protect cardholder data
2. Do not use vendor-supplied defaults for system passwords and other security parameters
3. Protect stored cardholder data
4. Encrypt transmission of cardholder data across open, public networks
5. Use and regularly update anti-virus software or programs
6. Develop and maintain secure systems and applications
7. Restrict access to cardholder data by business need-to-know
8. Assign a unique ID to each person with computer access
9. Restrict physical access to cardholder data
10. Track and monitor all access to network resources and cardholder data
11. Regularly test security systems and processes
12. Maintain a policy that addresses information security for employees and contractors

The complete PCI DSS ruleset is pubslihed here: https://www.pcisecuritystandards.org/document_library

The compliance with these rules is checked as part of a PCI DSS certification. 

Evidence is provided

• either by means of questionnaires which you must fill out. These questionnaires are referred to as  SAQ (self-assessment questionnaire).
  • The questionnaires are divided into different classes depending on how you process credit card data (SAQ A, SAQ A-EP, ... up to SAQ D).
• Instead of the questionnaire, a personal PCI DSS audit may also be required

However, BNP and Axepta Platform are annually audited and certified according to PCI DSS Level 1 - the most strict PCI DSS level.