The quantity of heat required to change the temperature of 1 g of a substance by 1⁰c is defined as

Specific heat is the quantity of heat required to change the temperature of 1 gram of a substance by 1 degree Celsius. It is the amount per unit mass that is required to raise the temperature by one degree Celsius. Every substance has its own specific heat and each has its own distinct value. The units of specific heat are joules per gram-degree Celsius (J/f C) and sometimes J/Kg K may also be used.

The teacher is mostly talking about the distillation of a mixture