The "F" in all of them mean "Frequency". The other letters denote the
segment of the spectrum, and it's not a code. Each are the first letters
of a real word, that describes where in the spectrum the segment is.
The caveat is that I've never heard of "VF", you're missing "VHF" (after
"HF") and unless there's a new meaning "EMF" is "electromagnetic force"
and doesn't belong with the others.
Since you have the right ordering, then figure it out yourself.
If at one end the frequencies are lowest, and the other end the frequencies
are highest, then what in the world might "ELF" mean?
Make an obvious guess, and that may be the key to the rest.