Negative feedback means that a factor within a control system has negative influence on itself. Example: In a biotope there are a certain number of foxes and prey animals like hares and mice. When the number of foxes increases, they reduce the prey animals. As they now have less food, also the foxes get less. And so the prey animals can multiply again. Negative feedback thus tends to lead to a stable balance.
A positive feedback on the other hand means that a factor strengthens itself and so can run out of any balance. An example of positive feedback in ecology: A plant has become rare in a biotope. Therefore its pollinators hardly ever come there. As a consequence the plants often stay without pollination and so get reduced in number.
The divers know positive feedback from the buoyancy control device (the inflatable jacket): If you inflate it without caution, you get up, the pression gets lower, the jacket expands, the buoyancy gets more positive, you get upwards more quickly. And suddenly you find yourself at the surface and did not want to go there.
French: rétroaction (negative / positive)