The specific heat of a substance my be broadly defined as the amount of heat required to raise the temperature of its unit mass through 1 degree. All the liquids and solids have one specific heat only. But a gas can have any number of specific heats depending upon the conditions, under which it is heated.

Specific heat at constant volume is the amount of heat required to raise the temperature of a unit mass of a gas throught 1 degree, when it is heat at constant volume.

Specific heat at constant pressure is the amount of heat required to raise the temperature of a unit mass of a gas through 1 degree, when it is heated at constant pressure.
The ratio of specific heat at constant pressure Cp and specific heat at constant volume Cv is always more than one.