A wave that (a) propagates in a transmission medium, (b) has a velocity determined by the launching conditions and the physical properties of the medium, and (c) may be a longitudinal or transverse wave. Note 1: For the purposes of this definition, free space may be considered a medium, although it is not a physical medium. Note 2: A traveling wave is not a wave that is reduced to a standing wave by reflections from a distant boundary. Note 3: Examples of traveling waves are radio waves propagating in free space, lightwaves propagating in optical fibers, water waves on the surface of the ocean, and seismic waves.