An explosive booster acts as a bridge between a low energy explosive and a low sensitivity (but typically high energy) explosive. It increases the energy of an initiating explosive to the degree sufficient to trigger the secondary charge.

For example: An initiator (such as detonation cord, shock tube, or cannon fuse) does not have the energy to trigger large high explosive charges (such as PETN, TNT, or ANFO), so a booster is used to upgrade the energy so that the main charge is activated.

Explosive boosters are typically constructed by mixing high sensitivity and high energy compounds at various ratios.

When encountered in connection with artillery shells or air dropped bombs, such a device is called a gayne.