Amazon SNS (Simple Notification Service) is a cloud-based messaging service provided by Amazon Web Services (AWS). It allows users to send messages or notifications to a large number of recipients quickly and efficiently. This service supports various communication protocols, including email, SMS, and mobile push notifications, making it versatile for different applications. With Amazon SNS, developers can create topics to which subscribers can subscribe. When a message is published to a topic, all subscribers receive the notification simultaneously. This feature is useful for applications that require real-time updates, such as alerts, news, or system notifications.