In SQS, a queue is a list of entries. An entry is a blob of data. When you create a queue, it's empty until you put entries on it. You can then read the entries you put on the queue. Entries remain on the queue until you explicitly delete them. The ordering of the queue is FIFO (First In, First Out). However, because access to the queues is heavily cached for performance reasons, Amazon does not guarantee FIFO access--occasionally, SQS requests may return results in a slightly different order than FIFO.