What is PCI compliance?
The card industry's security rules for any business that takes cards. They cover how card numbers are handled and stored.
Most small businesses meet them with a yearly questionnaire and secure card readers. Your processor can charge a monthly fee if the questionnaire isn't done, so it's worth checking your statement for one.
For example
Once a year, your processor asks you to fill out a short security questionnaire about how you take cards. Finishing it is part of PCI compliance.