AWS SQS stands for Amazon Simple Queue Service. It is a fully managed message queuing service provided by Amazon Web Services (AWS). SQS enables you to decouple the components of your application by allowing them to communicate asynchronously. It provides a reliable, scalable, and highly available platform for sending, storing, and receiving messages between software components.

Here are some key features and concepts related to AWS SQS:

1. Messages: SQS is used to send messages between distributed systems or microservices. A message in SQS can contain up to 256 KB of text in any format.

2. Queues: Messages are stored in queues within SQS. A queue acts as a buffer between the sender and the receiver. When a sender sends a message to a queue, it becomes available for the receiver to retrieve and process.

3. FIFO Queues: SQS offers FIFO (First-In-First-Out) queues that preserve the exact order of messages. FIFO queues are designed for applications that require strict message ordering and deduplication.

4. Visibility Timeout: When a message is retrieved from a queue, it becomes temporarily invisible to other consumers. This is known as the visibility timeout. If the consumer successfully processes the message within the timeout period, the message is deleted from the queue. Otherwise, the message becomes visible again for other consumers to retrieve.

5. Long Polling: SQS supports long polling, which reduces the number of empty responses by allowing the receiver to wait for a message to arrive in the queue before returning a response. Long polling helps reduce costs and latency in applications that have low message volumes.

6. Message Retention: SQS stores messages redundantly across multiple availability zones to ensure high durability. By default, messages are retained for a maximum of 4 days, but you can configure the retention period up to 14 days.

7. Dead-Letter Queues: SQS allows you to set up dead-letter queues, which receive messages that couldn’t be successfully processed after a certain number of retries. Dead-letter queues are useful for troubleshooting and handling failed messages.

8. Integration: SQS can be integrated with other AWS services like AWS Lambda, Amazon SNS, and Amazon EC2, enabling you to build complex distributed architectures.

SQS provides reliable messaging and helps in building scalable, fault-tolerant, and loosely coupled systems. It allows different components of an application to communicate asynchronously and ensures that messages are reliably processed even in the face of failures or spikes in traffic.