Consider the standing wave on a guitar string and the sound wave generated by the string as a result of this vibration. What do these two waves have in common

As the string vibrates, it "moves" the particles in the air, generating what we know as a soundwave.

Because this soundwave is generated by the wave-like motion of the string, makes sense that the soundwave will have some characteristics in common with the standing wave on the guitar string. This means that both waves will have the same normal modes. (So if the principal mode of the vibrating string has a frequency of 440hz, to soundwave also will have that main frequency, and we will hear an A). You can hear almost all the normal modes when you pluck a guitar string, particularly in music, these are called "overtones" or "harmonics"