Recently PRI's The World aired a segment entititled "What Constitutes a Famine?". In the story they explored the reasons why governmental agencies have been reluctant to declare famine in Somalia, which is currently in the midst of a severe food emergency.
Reporter Rhitu Chatterjee asked Molly Brown, a research scientist at Biospheric Sciences Branch, NASA Goddard Space Flight Center, to explain why a famine had yet to be declared in Somalia. Molly explained that one of the reasons is that the word "famine" is sort of a poltiical trump card to activate certain resources. Once those resources have been depleted, what do you do if the next year is even worse? You can read the entirety of the story on The World's website.