ANSWER: Texture.
EXPLANATION: Texture refers to the surface quality of an artwork and the way it looks or feels like it could be touched. In this case, the wave pattern likely has a texture that resembles the texture of actual waves, with different areas of the pattern appearing smooth or rough like the surface of the ocean. This gives the illusion of depth and movement in the artwork, bringing it to life and creating a more engaging sensory experience for the viewer. The use of texture is therefore a key element in creating the wave pattern and enhancing the overall visual appeal of the artwork.