Think of the harmonic as wave that can be systematically divided into smaller waves. The simplest wave is a pure tone referred to as a sinusoid. Any wave can be broken into a series of different frequencies. A harmonic is an electrical current that is accompanied by a frequencies that are integer multiples of the fundamental power.
Pay attention to electrical noises and buzzing. These annoying noises are actually harmonics Electrical power generates voltage waveforms that resonate at a certain frequency. The standard in the United States is 60Hz or 60 cycles per second. The goal is to generate a pure waveform, but this can begin to break down into smaller increments. In electronic terms, this is referred to as harmonic distortion or harmonic pollution.
Substitute musical terms for electrical terms. Harmonics in music also refer to sounds that are as multiples of the same frequency. However, musicians don't speak in terms of frequencies. Harmonics are thought of as "overtones." Harmonics are what give particular instruments their sound quality or timbre.They refer to musical intervals in terms of numbers. If the fundamental pitch and first harmonic is A 440Hz, the second harmonic resonating at 880Hz is an "octave" above the fundamental tone. The third harmonic is an octave and 5th above the original pitch and the third harmonic is two octaves above.
Play harmonics on the guitar. Guitar players know that there are harmonics all over the guitar and many players incorporate harmonics into their technique. However, anyone can play harmonics on a guitar. Play the open string. This is the fundamental tone. Play the harmonic at the 12th fret by holding your finger at the 12th fret without pressing down. This is the second harmonic, which is an octave above the original pitch. The third harmonic is at the 7th fret and the fourth harmonic is as the 5th fret.