Most of use know WiFi can be done on bands other than 2.4 GHz.
But how many are there? Two? Three? More?
Here is a place for more information without too much heady tech.

List of WLAN channels
However, you will have a hard time finding routers and adapters that cover more than three bands.

The main reason for using other bands is to avoid interference in a urban location. Do not expect to use any unlicensed band for long range wireless.

Do you use any of the other bands other than 2.4 GHz and 5 GHz?
Why? How?
I had a wireless bridge once that worked on the 900MHZ band which is the same as the cordless home phones a ways back. It was made by RCA and ALLOWED for you to connect to dial-up over wireless connection. Similar to this DEVICE linked here, but mine was a different model that I am unable to find in the QUICK search. https://www.ebay.com/itm/RCA-Wireless-Modem-Jack-RC930-Caller-ID-Compatible-New/183718509154?epid=22025376974&hash=item2ac679fa62:g:UfUAAOSwQrVb4VZU

As far as other bands/frequencies with modern electronics though. I believe you would need to get a FCC license and permission to use other than the standard home use bands even if its a focused radio signal coffee can to coffee can wifi bridge.