The detonator is used

A detonator (also known as a blasting cap) is a small, sensitive primary explosive device used to trigger a larger, less sensitive secondary explosive, known as the main charge.

In chemistry and ballistics, explosives are often categorized by their sensitivity. High explosives like TNT, RDX, or ANFO are relatively stable and cannot be easily ignited by a simple flame or spark; they require a high-velocity shockwave to detonate. The detonator contains a small amount of sensitive primary explosive (like lead azide or mercury fulminate) that reacts to a trigger (heat, friction, or electric spark) and creates the necessary shockwave to initiate the main charge. While some specific types of detonators include a delay element to control the timing of blasts, the fundamental purpose of any detonator is the initiation of the explosion.