In Amateur radio, the foundation license is the entry level license. A licensee gets a M3 Callsign. The foundation exam is very easy to pass, so there are many newcomers to the hobby that are a bit dim. A new colloquial term is therefore needed to describe a frequency that has many new licensees on it, aka the blind leading the blind.
So the term "foggy" seems to fit the bill, as the more M3's on a frequency, the denser it gets.
Two M3's on a VHF repeater talking about a crystal oscillator, and one says that a crystal is a living organism, as it has a heart beat at the frequency stamped on the tin. Another M3 joins in and thanks them for the explanation as to how he got detected by the TV license detector van, as his TV was switched off, so it must be true about the heart beat. The repeater was foggy.