> To simplify, it is any temporary support used during construction. <
Nope, it is a permanent part of the structure. It is not a jig.
I still dissagree. A Crutch can be left in or removed but is still a temporary support until the structure is completed. A crutch does not serve an integral support on the finished model. I guess some terms differ from place to place and personal experiences.
We can agree that a crutch holds key parts in place for proper alignment.