Definitions for "Helium flash"
A rapid burst of nuclear reactions in the degenerate core of a moderate-mass star in the hydrogen shell-burning phase. The flash occurs when the core temperature reaches a sufficiently high temperature to trigger the triple-alpha reaction.
Somewhat sudden and rapid ignition of helium in the electron-degenerate core of a star, after which the star settles down to fusing helium quietly into carbon.
The rapid onset of helium fusion in a red giant star.