Definition of low explosive in US English:

low explosive

noun

  • An explosive substance which ignites and decomposes at a rate similar to or slower than that of gunpowder; (in later use) specifically one which explodes at a rate slower than the speed of sound; (as a mass noun) material of this kind; contrasted with "high explosive".

Origin

Late 19th century; earliest use found in Gold Mines & Mining in California.