> Generally referred to

Sure, people may sloppily call it a failure, but then they miss out on a useful distinction which would help them create more robust software.

A bolt being under-engineered for its intended usage is a design error. When it breaks, that's a predictable (but unfortunate) mode of operation of the design, not a failure. (It has inadvertently been designed to act as a frangible link.)

The reason it's important to distinguish between the two cases is that we use different methods to deal with them.