Vault is a dedicated secrets manager that securely stores an application's sensitive data, such as usernames, passwords, and API keys, separate from code. This approach improves security by reducing the risk of accessing credentials alongside source code. Vault provides features like secret versioning, automation of credential rotation, and rolling of encryption keys. It integrates with various infrastructure services, including Microsoft Azure, Google Cloud, and RabbitMQ. A PHP application can use Vault to manage secrets securely, retrieving, updating, and deleting them as needed. The application uses the Slim Framework for routing and a DI container for dependency injection. To interact with Vault, the application sets authentication using a token or other methods like username and password. The tutorial demonstrates how to create, update, read, and delete secrets in Vault using PHP, providing a secure way to manage sensitive data.