Explanation: The emission of electrons from a material due to the impact of high-velocity electrons is known as **secondary emission**. When energetic primary electrons strike a surface, they transfer kinetic energy, dislodging and ejecting other electrons from that material. These ejected electrons are called secondary electrons. This phenomenon is fundamental to the operation of many vacuum tube devices, such as electron multipliers and some types of amplifier tubes, which were essential components in early radio and radar equipment. **Primary electron emission** refers to the initial source of electrons, such as thermionic emission (from a heated cathode), photoelectric emission (from light), or field emission. It describes the *creation* of the initial high-velocity electrons, not their subsequent impact. **Mimetic emission** is not a recognized term in electronics or physics, making it an incorrect option.