HashiCorp Vault is a centralized platform for managing secrets (API keys, database credentials, cloud credentials, encryption keys) across infrastructure. Instead of scattering secrets in config files, environment variables, or password managers, Vault centralizes them, controls access, audits usage, and can rotate them automatically. You deploy Vault servers, define authentication methods (AppRole, JWT, LDAP), configure secrets engines (database, AWS, PKI), and integrate with applications and CI/CD systems. Applications request secrets from Vault; Vault authenticates the application and returns the secret.