[CobrastanJorji]

That's sound. Very lossy sound, presumably at a very low frequency, but sound nonetheless. There's a physical medium, and a signal is being passed through it via tennis ball pressure. If you had a sufficiently dense field of tennis balls, you could visually observe the wave moving across it as the field compressed (in the direction the signal is traveling) and then uncompressed, cyclically.

A good trick to telling the difference is thinking about the direction of the frequency. Frequency is a back and forth movement. If it's going back and forth in the direction the overall signal is moving (like a tennis ball going faster towards the destination and then more slowly or backwards, or like the wall at the source of the signal vibrating towards the other wall), that's a physical wave. If the back and forth movement is happening in an entirely different plane, that's like an electromagnetic wave.

[jasonwatkinspdx]

So just to be clear, as it seems the other poster is quite confused, whether waves are "physical" or not is independent of whether their traverse waves or density waves. Sound is an example of density waves. The waves at the interface between the ocean and the air are gravity waves. Both are physical.

EM waves are physical as well, they just are in the EM field itself, rather than having a medium like matter.