1)The mean energy transferred between the two system as a result of pure thermal interaction is called Heat.It is the transfer of energy from the higher temperature object to a lower temperature object.
2) The total amount of energy transferred as heat is conventionally written as Q for algebraic purposes. Heat released by a system into its surroundings is by convention a negative quantity (Q < 0); when a system absorbs heat from its surroundings, it is positive (Q > 0).
3) Heat is similar to work as both represent ways of transferring the energy.
4) Heat is not an intrinsic property of the system that is we can not say that a system contains a certain amount of Heat. It is the transfer of heat either out and in which matters Unlike properties like pressure,temperature and internal energy ,Heat is a not state function. Like work, it exists only as energy in transit from one system to another or between a system and its surroundings. When energy in the form of heat is added to a system, it is stored as kinetic and potential energy of the atoms and molecules in the system
6)It is a measurable quantity.Direct measurement is by calorimetry and is the primary empirical basis of the idea of quantity of heat. The transferred heat is measured by changes in a body of known properties, for example, temperature rise, change in volume or length, or phase change, such as melting of ice