PCI DSS stands for the Payment Card Industry Data Security Standard. PCI compliance is a set of regulations for companies who accept credit card payments.
Companies are required to conform to these regulations to ensure that sensitive card data is not compromised by their systems and servers. This ensures the Internet and shopping online is secure and reduces the number of fraudulent transactions.
These regulations could also be considered best practice for all online companies to ensure they do not expose themselves to unnecessary risks even if they are not taking online payments they could still benefit by ensuring security vulnerabilities are eliminated and their data is safe from being hijacked.