Well, first we have to consider that when we talk about positive and negative feedback, usually we refer to homeostasis, which's a kind of balance our bodies do regarding physiological processes.
Having this in mind, we use the term negative feedback to signal the balance of nutrients (e.g. oxygen, minerals), pressure, and temperature, our blood does to achieve the normal equilibrium of this in our body.
In the same way, when we say positive feedback, we refer to those processes that our body carries out to keep or maintain the influence of a stimulus.
