I've been looking for an answer to this for the past couple of hours and can't find anything on the matter. (Yes, I've read this What radio frequencies are used for intercom in formation flying? , but it didn't answer my question, as I'd like to know about frequencies that are not in use by any authorities or organisations and are not used for anything official, such as search and rescue).
A pilot mentioned to me she "created" frequencies to talk in private with her mate (air-to-air interpilot). I found one link that says pilots sometimes use unallocated frequencies to chat , so I assumed she meant that, but I've just read on AOPA that all 760 channels available in the VHF aviation band are actually allocated (I'm assuming in the USA, as the reference is an FAA circular) even if some are not used at all times.
So, can you "create" a private frequency? If I'm right to assume that that makes no sense, can you join a private frequency (do they exist??) or use an unallocated one to chat privately? In case it's the latter, how does that work if all frequencies are allocated already (or is that just in the USA)?
Thanks a lot for your help