First in First Out delivery - order in which messages are sent and received is strictly preserved

Exact-once processing - no duplicates

One of the main difference between Standard and FIFO, which also explain the differences in ordering and delivery, is that Standard Queues support Unlimited throughput - unlimited transactions per second (TPS) - while FIFO is High Throughput and supports up to 300 messages per second ( send or receive or delete all counted together) - you can get to 3000 if you batch 10 messages per operation.