What do people mean by "measurable definition?"

It is reasonable to infer that the person who wrote that was discussing "a clear definition that supports measurable metrics that would allow two like systems to be compared against each other", and decided that the title "A Measurable Definition of Resiliency Using 'Mission Risk' as a Metric" was already a wordy enough title without wording it as "A Definition That Supports Measurable Metrics That Would Allow Two Like Systems To Be Compared Against Each Other of Resiliency Using 'Mission Risk' as a Metric". It is within the realm of normal English usage to precede a noun with an adjective that does not, strictly speaking, refer to that noun, but to things connected to it, especially in a context such as a title where brevity is a concern, and there are further opportunities, such as an abstract, to use more precise language. See such terms as "metonymy".