What is negative feedback?
Negative feedback occurs when the response to a stimulus has the effect of counteracting or reducing the effects of the original stimulus. For example, if you feel cold, your response to this stimulus may be to put on a jumper - this response reduces/eliminates the original stimulus of feeling cold. Negative feedback systems are also called steady state control systems, as they return the body to a steady state.
Negative Feedback Analogy
An analogy which can be used to describe how negative feedback loops occur is that of an AC (air-conditioning) system in a room. Let's say that the temperature is set to 22 degrees Celsius. On a warmer day when the temperature rises above 22 degrees, the thermostat automatically switches the air conditioner on. When the room becomes cooler than 22 degrees, the thermostat then switches the air conditioner off when it reaches its target temperature. The process is repetitive so that the air temperature remains relatively constant.