What is the transfer of thermal energy from one object to another due to a difference in temperature is known as?

The transfer of thermal energy when particles of a fluid move from one place to another is convection. Temperature is a measure of how hot or cold an object is compared to a reference point.

Another Answer

No. Heat (the term, 'thermal energy', is obsolete) is defined as 'energy in transit from a warmer body to a cooler body'. So a temperature difference is necessary for heat transfer to take place.

It is not heat it is convection.