The terms "undetectable sound wave" and "undetectable light wave" are not commonly used in scientific contexts because they imply waves that cannot be detected by any means, which goes against the fundamental nature of waves.
Sound waves and light waves are forms of energy that propagate through a medium (such as air or vacuum in the case of light). They can be detected and measured using various instruments and human sensory organs.
In the case of sound waves, they are typically detected by our ears or specialized microphones. Sound waves with frequencies below the audible range for humans (less than 20 Hz or greater than 20,000 Hz) are called infrasound and ultrasound, respectively. Although we cannot perceive these frequencies directly, we can still detect and measure them using appropriate equipment.
Similarly, light waves are typically detected by our eyes or specialized light-detecting devices, such as cameras or sensors. The visible light spectrum is the range of light frequencies that our eyes are sensitive to (roughly 400 to 700 nanometers). However, there are light waves with frequencies beyond this range, such as infrared and ultraviolet, which can be detected and measured using appropriate detectors.
If there were truly "undetectable" sound or light waves that couldn't be detected by any means, it would be impossible for us to conceive what they would look or sound like. Our understanding of the physical world is based on our ability to detect and measure waves, so anything beyond the realm of detection would lie outside our current understanding and observational capabilities.