This document provides definitions for key terms related to PCI compliance. It defines terms like Approved Scanning Vendor, which certifies an organization's compliance; Audit Log, which records system activities; Cardholder Data, which contains customers' payment information; and Cardholder Data Environment, which includes all systems that store or process payment data. It also defines security concepts like Encryption, File Integrity Monitoring, Firewalls, Intrusion Detection and Prevention Systems, Penetration Testing, and Private Networks.