Hydroponics is the process of growing plants in a soil-less environment, and adding nutrients through a solution fed directly to the plants. This can be achieved by suspending the plants directly in water, or by planting in gravel or any other form of growing media.
Aquaculture is the farming of fish populations. By combining the two, the waste produced by the fish, becomes a natural fertilizer for the plants, which in turn filters the water from the waste that would be harmful for the fish. The water can thus be re-circulated and conserved.