Hydroponics is raising plants in water rather than soil.
Aquaponics takes that concept a step further. Raise fish or other aquatic organisms in the water and you can make a largely self-sustaining system. Fish waste adds nutrients to the water, feeding the plants.
And at the end of the day you can have tilapia with mixed greens.
(Link goes to an interesting writeup on myfreshlocal.com with an aquaponics system diagram and some ideas of how aquaponics can help grow fresh food in urban settings.)