Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Given that maximum air displacements are possible at the open end and none at the closed end, there are other, shorter wavelengths that can resonate in the tube, such as the one shown in Figure 17.28. Here the standing wave has three-fourths of its wavelength in the tube, or L = (3 / 4)λ′ , so that λ′ = 4L / 3 . Continuing this process reveals a whole series of shorterwavelength and higher-frequency sounds that resonate in the tube. We use specific terms for the resonances in any system. The lowest resonant frequency is called the fundamental, while all higher resonant frequencies are called overtones. All resonant frequencies are integral multiples of the fundamental, and they are collectively called harmonics. The fundamental is the first harmonic, the first overtone is the second harmonic, and so on. Figure 17.29 shows the fundamental and the first three overtones (the first four harmonics) in a tube closed at one end.


Question: The lowest resonant frequency is called the what?
fundamental
fundamental.