To understand what the 5 GHz Wi-Fi spectrum is, it is helpful to compare it with the 2.4 GHz and 6 GHz spectrums. Each of the three spectrums has a certain number of available channels, different speeds, and different ranges of Wi-Fi transmission.
The 2.4 GHz band has 3 non-overlapping 20MHz bandwidth channels and one 40MHz channel. The 2.4 GHz band is ideal for sending moderate amounts of data over long distances.
The 5 GHz band has 25 non-overlapping 20MHz channels, 12 40MHz channels, six 80MHz channels, and two 160MHz channels. Wi-Fi 5 devices only use the 5 GHz band. Wi-Fi 6 devices are capable of using the 2.4 and 5 GHz bands because they contain two radios, each of which can communicate over one of the two spectrums. The 5 GHz band is capable of delivering and receiving exponentially higher amounts of data but over shorter distances than 2.4 GHz.
Wi-Fi 5 operates exclusively on the 5 GHz channel. Because the "generation" and the channel share the number 5, many people are misled into thinking that the numbers match on purpose. They do not. IEEE is the governing body that has established what it calls the "802" standards for Wi-Fi. However, because their labels were hard to remember, manufacturers began to describe each iteration of Wi-Fi standards using just a number. To clarify which generation corresponds with which set of standards as well as which channels each generation uses, see below:
Wi-Fi 1 = 802.11b that operates on 2.4 GHz
Wi-Fi 2 = 802.11a that operates on 5 GHz
Wi-Fi 3 = 802.11g that operates on 5 GHz
Wi-Fi 4 = 802.11n that operates on 2.4 and 5 GHz
Wi-Fi 5 = 802.11ac that operates on 5 GHz
Wi-Fi 6 = 802.11ax that operates on 2.4 and 5 GHz
Wi-Fi 6e = an extension of Wi-Fi 6 that operates on 2.4, 5 and now 6 GHz