[Ref SKYbrary]

What’s thermal runAway?  (p.s NOT thermal runway!!!)

Thermal runaway is a situation that occurs when an increase in temperature changes the conditions of a reaction in a way that causes a further increase in temperature – It is a kind of uncontrolled positive feedback.

In other words, if a process is accelerated by an increase in temperature and that acceleration results in the release of additional energy which further increases the temperature, a state of thermal runaway is said to exist. This state can lead to an explosion, fire or other destructive result.