>"...is the peculiar manner in which the Fourier series of a piecewise continuously differentiable periodic function behaves at a jump discontinuity. The nth pa

>"...is the peculiar manner in which the Fourier series of a piecewise continuously differentiable periodic function behaves at a jump discontinuity. The nth partial sum of the Fourier series has large oscillations near the jump, which might increase the maximum of the partial sum above that of the function itself" I'd say the minimum qualifications of understanding this sentence adequately is: - knowing the basic terminologies of calculus to understand what "piecewise continuously differentiable" means - knowing that the Fourier series is some sort of infinite series, which you can get from context if you already know that infinite series is a thing, from Taylor series, which you'd know from calculus from the above requirement.