I've also seen them called jewellers saws, I guess it depends which school you went to. Both of mine have a limited throat, about three inches, but if you need more you can use the same blades in a normal fretsaw frame. You do need to do the wingnuts up a bit tighter than usual or the blade will slip, which tends to be hard on them.
The blades seem to be available in more than one size, I have them ranging up to nearly a normal fretsaw blade and down to really fine. A very handy device.
John