It is also called a bow saw. Folding or not folding would depend on how the handle is constructed, but the blade can easily be removed for safer storage and handling (provided you've got a tube or something to stuff the blade into).

http://en.wikipedia.org/wiki/Bow_saw

I've seen variants of these where the handle and blade would fold into a single lightweight tube - but of course with some minor reduction in size and robustness.