Definition: a smooth emulsion of chocolate and warm cream, used as a filling, glaze, drip or whipped frosting depending on the ratio.
Ganache (gah-nahsh) is one of those techniques that feels fancy and is really just chocolate and cream stirred together. The ratio decides the job: more chocolate sets firm for a truffle or a filling; equal parts gives a pourable glaze or a chocolate drip; more cream, whipped once cool, makes a light frosting. Warm the cream, pour it over chopped chocolate, wait a moment, then stir from the middle out until glossy.
In practice: let a drip ganache cool to just-pourable — too warm runs to the base, too cool won’t drip.
Related:crumb coat,folding.