FODMAP is an acronym for "Fermentable Oligo-, Di-, Monosaccharides And Polyols". These are partially or completely malabsorbed in humans. The bacteria in the colon ferments them wich leads in some people to constipation, bloating, stomach pain or diarrhea – IBS symptoms.

The FODMAP diet temporarily eliminates the foods with a high content of such carbs.

Find out more on wikipedia or google: "FODMAP diet"