To maintain cells, tissues and entire organisms within their biological tolerance limits, various mechanisms have evolved. Homeostasis is really the combined result of all of these, a failure of any one of them can result in the death of an individual. For now, we will focus on functional mechanisms of homeostasis, but students should not consider that these in isolation will maintain life. Essentially, feedback occurs when the response to a stimulus has an effect of some kind on the original stimulus. The nature of the response determines how the feedback is 'labelled'.
Negative feedback is when the response diminishes the original stimulus.
Positive feedback is when the response enhances the original stimulus. Negative feedback is most common in biological systems. Positive feedback is less common, which is understandable, as most changes to steady state pose a threat, and to enhance them would be most unhelpful. The hungry baby continues to suckle, stimulating more milk release until she stops. All the fruit quickly becomes ripe together.