This term is defined in ECSS-E-ST-35C Rev. 1 as
first element in an explosive chain that, upon receipt of the proper impulse, produces a deflagrating or detonating action

This term is defined in ECSS-E-ST-50-51C as
SpaceWire node that starts a transaction by sending a command to a SpaceWire node

This term is defined in ECSS-E-ST-33-11C Rev.1 as
basic component located upstream of an explosive train, from which originates a transformation of mechanical, electrical or optical energy, the effect produced being a combustion, deflagration or detonation.