A stateless web service is a type of service that does not retain any information about previous interactions. Each request from a client is treated independently, meaning the server does not store any session data between requests. This design simplifies the server's architecture and improves scalability, as it can handle multiple requests without needing to manage user states. In a stateless web service, all necessary information must be included in each request. This often involves using formats like JSON or XML to send data. Popular protocols for stateless web services include HTTP and REST, which are widely used in modern web applications.