(1) A form of energy that is transferred from between objects due to a temperature difference; the thermal motion of atoms and molecules
(2) Oestrus; a condition where a mammal is aroused sexually, i.e. when fertile and eager to mate
In physics, heat is a form of energy transferring between objects because of a difference in temperature. Heat transfers from one that has higher temperature to another that has lower temperature. Transfer may be directly (e.g. contact) or indirectly (e.g. via convection circulation). For chemical systems the sign for heat flow into the system is positive, because this process increases the internal energy of the system. Heat flowing out of the system is defined to be negative, since this process decreases the internal energy of the system.
In zoology, heat is synonymous to oestrus, which is that phase of the sexual cycle of female animals characterized by the willingness to permit coitus.