Final answer:
A single, pure tone with no harmonics or overtones is called a fundamental, which is the lowest-frequency resonance and most intense aspect of a sound.
Step-by-step explanation:
A single, pure tone that contains no harmonics or overtones is known as a fundamental. This is the lowest-frequency resonance of a system and is often the most intense. Unlike the fundamental, harmonics are multiples of the fundamental frequency. The second harmonic is the first overtone, and the first harmonic is actually the fundamental itself. While the fundamental and overtones can be present simultaneously, producing the unique timbre of an instrument, a pure tone consists only of the fundamental, without any additional overtones or harmonics, leading to what is often perceived as a very clean and clear sound, important in the science of hearing.