What is the actual definition of the TM mode? A typical definition that I've come across is that there is no Magnetic field component in the direction of wave propagation. As it is an EM wave, according to that definition the Magnetic field should be in the plane normal to the direction of propagation. Recently I saw in some books, it states that if a TM wave is traveling in x direction, the magnetic field component should be y direction (i.e Hy is the only nonzero component, with Hx=0 & Hz = 0). (The other only nonzero components being Ex & Ez). Is it always the case for TM waves? Or is this for some special condition?