The equation $r = extbackslash sqrt{x^2 + y^2}$ represents the relationship between the Cartesian coordinates (x, y) and the polar coordinates (r, θ) of a point in a two-dimensional plane. The variable 'r' represents the radial distance or magnitude of the vector from the origin to the point, while the variables 'x' and 'y' represent the horizontal and vertical coordinates of the same point in the Cartesian coordinate system.