What is the definition of The heat required to raise one gram of a substance by one degree Celsius?

In olden days, scientists had not attained a state to realize the relation between heat and mechanical energy. So in that situation they have coined a Word calorie for the unit of heat. One more point that only cgs system was active in those days. Calorie is defined as the heat required to rise the temperature of one gram of water through one degree celcius. If s calorie of heat is required to rise the temperature of one gram of any substance then s is said to be the specific heat of the substance.

Later science got good advancement, heat was also measured in terms of the unit of mechanical energy ie joule. So the amount of heat energy in joules to rise the temperature of one gram of water was found to be 4.18 joule. Hence mechanical equivalent of heat is said to be 1 calorie = 4.18 joule

So the heat energy in joule required to rise the temperature of one kilo gram (not one gram) of substance is defined as the specific heat capacity. Capacity has been added along with specific heat. Many modifications gradually came into the scene. Absolute scale was found and unit for temperature kelvin got introduced.

So just heat, one gram and celcius all have become obsolete. They have been replaced by energy, one kilo gram and kelvin respectively. This is also to be treated as evolution in probing the secret of nature in a systematic way.

Hence in case of water, its specific heat capacity was found to be 4180 joule/kg/K.