The .pem file extension stands for Privacy-Enhanced Mail and is a common file format used to store cryptographic keys and certificates. These files are typically encoded in ASCII text format, often using Base64 encoding, which makes them human-readable, although the content itself is usually binary data (like an X.509 certificate or a private key) wrapped in PEM headers and footers (e.g., '-----BEGIN CERTIFICATE-----' and '-----END CERTIFICATE-----'). PEM files are widely used in SSL/TLS communications, digital signatures, and various security protocols. They can contain public keys, private keys, certificate chains, or a combination thereof. Because they are text-based, they are easily transferable across different systems and are the standard format used by many open-source cryptographic libraries, such as OpenSSL. While the name suggests email security, their application has expanded significantly to cover general public key infrastructure (PKI) needs across web servers, VPNs, and application security.