What is heat? Heat is a form of energy that can be transferred between a system and its surroundings because of a temperature difference between them.
How is heat transferred? The transfer of energy by heat flow is caused by molecular collisions; this type of interaction is termed a thermal interaction.
When does heat transfer stop? When a system reaches thermal equilibrium with its surroundings---the system and surroundings have the same temperature.
For two systems at the same temperature and in thermal contact, a
steady-state temperature difference cannot be generated.