A signal source is connected to a load via a transmission line of length l. For the case of a uniform line with TEM propagation, a sinusoidal steady state solution for the instantaneous voltage V(z)eʲωᵗ at a position z is given by

V(z)eʲωᵗ=V₁(0)e−αᶻ eʲ⁽ωᵗ−βᶻ⁾) +Vᵣ(0)eαᶻ eʲ⁽ωᵗ⁺βᶻ⁾

Explain the significance of 'TEM propagation' in the above statement.