Wi-Fi specifications for iPhone, iPad and iPod touch
802.11 compatibility and frequency band: 802.11ac, 802.11n, 802.11a, 802.11b/g, and 2.4GHz or 5GHz.
Physical Data Rate (PHY): The highest rate at which a client can transmit data over Wi-Fi.
Channel bandwidth: The maximum channel bandwidth that is supported. Starting with 802.11n, channels can be combined to create a wider channel that allows for more data to be transmitted during a single transmission. With 802.11n for 5GHz band, two 20MHz channels can be combined to create a 40MHz channel. With 802.11ac for 5GHz band, four 20MHz channels can be combined to create an 80MHz channel.
MCS index: The Modulation and Coding Scheme (MCS) index defines the maximum transmission rate at which 802.11ac/n devices can communicate. 802.11ac uses Very High Throughput (VHT) and 802.11n uses High Throughput (HT) packets.
Spatial streams/SISO/MIMO: Each radio can send a specific number of independent data streams, called spatial streams, at the same time, which can increase overall throughput. Single input single output (SISO) uses a single radio and antenna, and multiple input multiple output (MIMO) uses multiple radios and antennas.