This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From: firstname.lastname@example.org (Jerry Irvine)
[Editor's note: This is paraphrased from Jerry's postings]
Flash in the pan ignition is used to ignite clusters of small black powder
rocket motors. It consists of a thin layer of black powder on a paper plate
under the motor nozles. The powder is ignited via a regular model rocket
igniter, such as an Estes Solar igniter. When the power ignites, the
burning particles and hot gasses from the 'flash' ignite the motors.
It is used to ignite clusters of 7-469 motors and reduces the number of
igniters needed to one.