Adding the viscous term to the eigenmode equation for this phenomenon gives the Orr-Sommerfeld equation.  
Adding the viscous term to the eigenmode equation for this phenomenon gives the Orr-Sommerfeld equation.  Rayleigh showed that in simple cases, a necessary condition for this phenomenon is that there be an inflection point in the velocity profile. Another common necessary condition for this phenomenon is a value of less than one-fourth for the Richardson number. This phenomenon is responsible for the formation of high-altitude undulatus or "billow clouds" near jet streams, and it is suppressed by a parallel magnetic field if the AlfvÃ©n velocity exceeds the velocity change driving this instability. FTP, a vortex sheet at a velocity discontinuity is a simple case of what shearing instability named for British and German physicists?
Adding the viscous term to the eigenmode equation for this phenomenon gives the Orr-Sommerfeld equation.  
Kelvin-Helmholtz instability (accept shear instability or shearing instability before mention in the question)