harmonic
When considering a time-related signal in terms of frequency, it shows a more or less large number of harmonics in addition to the fundamental.
Harmonics are the integer multiple of the fundamental. Thus, the 1st harmonic, which is also the 2nd harmonic, has twice the frequency of the fundamental, the 2nd harmonic has three times the frequency of the fundamental, and so on.
The first harmonic of concert pitch "A" with a frequency of 440 Hz has 880 Hz, the second 1.360 kHz, the third 1.760 kHz, and so on. The fundamental together with the harmonics characterizes the sound.