My guess is that it is just an entirely made up term.
Intrinsic just means that it is a part of the central nature of something that makes it what it is.
For example, "mass" is an intrinsic property for all fermions. (afaik)
or, electric charge is an intrinsic property of all electrons.
So to be honest, I think the writer chose a great word to use there, because it is very vague.
The way I see it, it could really be any kind of field. It's unspecified, they would have to say "intrinsic electrical field" or magnetic, etc...
But, from a completely fantasy perspective in my opinion it sounds like you could interpret it as some unspecified "pure" field. Without requiring the normal methods of generating that field.
Like a gravitational field without requiring mass, or an electric field without any charged particles... just the field itself, thus "intrinsic field".
Currently I think it is impossible to do that, but then again, a photon is basically just alternating electric and magnetic fields by themselves.
Anyway from a sci-fi perspective that's what it sounds like the author may have had in mind. and it's kind of a cool idea IMO :D