A sound wave with no amplitude would be considered a silent or inaudible sound wave. In other words, it would not produce any detectable variation in pressure or displacement from the equilibrium position. The absence of amplitude implies that the wave does not carry any energy or cause any perceptible disturbance in the medium through which it propagates.
However, it's important to note that in reality, sound waves with precisely zero amplitude are rare or practically nonexistent. Even the faintest sounds have some amplitude, albeit extremely small. A truly zero-amplitude sound wave would be imperceptible and indistinguishable from silence.