What is the difference between hunger and appetite ?

Hunger is the need to eat. If you're hungry, you need food because your body is telling you so. It's sending you signals, like those rumbling stomach growls known as hunger pangs. Hunger cannot be controlled; it is instinctive. And for some individuals, ignoring hunger can cause serious consequences. Waiting too long to eat once hunger kicks in may mean the risk of low blood sugar and the wooziness and fatigue that come with it.  

Appetite is the desire to eat. Appetite occurs as a coordinated effort between your brain and your belly. When you feast your eyes on a delicious, delectable food, your mouth may water, and you can practically taste it and feel the textures on your palate. Even the mere thought of food can elicit the same emotional response. But unlike hunger, appetite can be ignored. And since appetite levels are greatly influenced by your brain, it is a learned behaviour, and you can even learn to control and change the level of your appetite.

source : http://www.medbroadcast.com/Channel/Weight-Management/Road-blocks-to-weight-loss/Appetite-vs-hunger

Simple,

Appetite is the desire to do something which you like or need

Hungry means an alarm for the need of food (Because the body need nutrients for the proper metabolism)

HUNGRY : bad feeling caused by need for food while

APPETITE : good feeling caused by presence of environmental and sensory  factors that makes you eat with you're not in need for example : presence of food and friends, or smell of food.

Eat in response to the needs of the body physiological and called eating in response to hunger, and between that eat not because our bodies need but because our souls crave, including all the sensations delicious food related when it passes the one-Khater us, for example, the taste and flavor of chocolate delicious, Faihs desire to eat it for this reason without there is a need to be physiological for it.

Hungry means as a result of metabolic/chemical  reactions your body seriously require nutrients and energy for various physiological functions of the body. If you dont eat at this stage, your body will consume stored nutrient but if this state persist wasting of body may occur. Appetite refers to state of sensory feeling that you need to eat something. sometime you are full but sensory forces drive you to eat something more so it is appetite.

Hunger need for Food to consume 

appetite is feeling of hungry even has half stomach full 

Agreed with experts. Hunger and appetite are totally different concepts but related as people eat for two reasons one is for hunger and other one is for appetite. Hunger is the need for food as the body requires food like fuel for functioning as chemical changes in the body related to a naturally low level of glucose in blood. Appetite is a psychological reaction to eat food when a delicious food is seen or smelt. When one is hunger appetite of any food may be good and when one is not hungry even delicious food will not create appetite.