Homeostasis refers to stability, balance, or equilibrium. The body attempt to provide a constant and fair internal environment. Homeostasis is commonly achieved via negative feedback loops that are characterized by their capacity to either increase or decrease a stimulus, constraning the ability of the stimulus to continue as it did preceding to sensing of the receptor.
Any homeostatic process that changes the direction of the stimulus is a negative feedback loop. The stimulus is not allowed to continue as it did before the receptor sensed it. If a level is too high, the body does something yo bring it down. If a level is too low, the body does something to raise it.