Here's why:

* Alternating nature: The key characteristic of AC is that the direction of the current flow reverses periodically. This creates a pattern that resembles a wave.

* Sinusoidal waveform: The most common type of AC is sinusoidal, meaning the current varies smoothly and periodically, following a sine wave pattern.

* Frequency: AC is characterized by its frequency, which refers to how many times the current reverses direction per second. This further reinforces the wave-like nature of AC.

While AC can be described as a "form" in the sense that it's a specific type of electrical current, the fundamental nature of AC is that of a wave.