Explain what SNS notification service is and what it is used for.

Amazon SNS (Simple Notification Service) is a managed notification service that allows sending messages (notifications) to subscribers or other applications.

Main features and purposes:

• Publishing messages to topics that various recipients subscribe to.
• Support for various delivery protocols: HTTP/HTTPS, Email, SMS, Push notifications, AWS Lambda.
• Used for implementing alert systems, mailing, and integration between services.

Example of use:

• Sending notifications about events in the application to users via SMS.
• Triggering Lambda functions upon receiving new messages.

Thus, SNS serves for scalable and reliable message delivery between components of distributed systems.