In the lower ionosphere of Venus, just nightward of the terminator, instruments on the Pioneer Venus Orbiter have revealed nearly coherent wave trains in the electron density. Ne temperature, Te, and in the east-west component of the magnetic field, BE. These waves exist primarily below 200 km. They have north-south wavelengths of the order of 150 km and amplitudes in Ne and Te of about a factor of 2 or 3. BE has an amplitude of about 30 nT but no net value averaged over the waves. A unique phase relationship exists between these three parameters. Ne and Te vary approximately, suggesting that the waves represent vertical plasma motions. Ne maxima and minima tend to occur at zero crossings of BE, i.e., within regions of vertical currents. The plasma pressure is roughly constant within the wave and is several times larger than the magnetic pressure. The wave energy is believed to be derived from the steep plasma pressure gradient at the terminator which accelerates ionospheric plasma nightward. The generation process is unknown, but it may involve gradient driven interchange instabilities, or shear instabilities produced by ion-neutral drag at low altitudes. Whatever their origin, the waves are important because they represent an energy sink for the transterminator flow that is largely responsible for the maintenance of the nightside ionosphere.