What? A queue that runs tasks FIFO.
Types?
- Serial – one at a time
- system-provided: main queue
- you can create your own
- Concurrent – 1+ tasks at a time
- system-provided: 4 queues (high, default, low, and background)
- you can create your own, but 4 system ones should be good enough
Note: iOS 8+ should use QoS instead.