Amazon Simple Queue Service (SQS) is a distributed queue system.
Amazon SQS enables you to send, store, and receive messages between software components.
An Amazon SQS queue is a temporary repository for messages that are awaiting processing.
The SQS queue acts as a buffer between the component producing and saving data, and the component receiving the data for processing.
This is known as decoupling / loose coupling and helps to enable elasticity for your application.
Amazon SQS is pull-based, not push-based (like Amazon Simple Notification Service (Amazon SNS)).