Feedbacks often set off a chain of changes, called a feedback loop, in the system. For example, the internal regulation of your body temperature is a negative feedback loop. A change in your body temperature triggers parts of the system(your body) to respond by increasing(shivering) or decreasing (sweating) the temperature and sending it back toward a steady state, thus suppressing change.
On the other hand, population growth can create a positive feedback loop. When more birth occur, the next generation has more people to have more babies. In time, these babies grow up to have more babies, who grow up to have more babies, and so on. Thus, positive feedback loops can lead to runaway effects-sending a system far from its steady state.
In the context of systems, the terms positive and negative don’t mean good and bad. In fact, positive feedbacks are often more dangerous than negative feedbacks because they move a system farther from stability.