Hi Adane

It would be interesting in what context you would want to use the answer? There are various conceptualizations - and also a definition by the WHO (2014):

"Mental health is defined as a state of well-being in which every individual realizes his or her own potential, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to her or his community. "

http://www.who.int/features/factfiles/mental_health/en/

Best,

Christian