The w-axis is an imaginary vertical line on a coordinate plane. In this problem, our region defined by g(y) and k(y) is being revolved around this axis.
Related terms
Coordinate Plane: A two-dimensional grid formed by two perpendicular number lines called axes.
Vertical Line: A straight line that extends infinitely up and down along its length.
Imaginary Line: A concept used to represent something that doesn't physically exist but helps us understand mathematical ideas.