In the wave model of light, light is described as an electromagnetic wave. In this model, what is "waving" are the electric and magnetic fields that propagate through space.
According to electromagnetic theory, light is composed of mutually perpendicular electric and magnetic fields that oscillate as they travel through space. These fields are perpendicular to the direction of propagation of the wave, forming electromagnetic waves.
As the light wave moves, the electric field and magnetic field interact with each other, continuously oscillating and generating energy that is transmitted through space. This oscillation of the electric and magnetic fields is what is referred to as the "wave" of light.
It is important to note that the wave model is just one way to understand and describe the behavior of light. Light also exhibits properties of particles called photons, and the dual nature of light is described by quantum mechanics. In the wave-particle duality concept, light can behave both as a wave and as a stream of particles depending on the experimental setup and observation.