Adverse yaw was explained by Jack, maybe you are refereing to dutch roll. Adverse yaw occurs in real airplanes and models. In models we tend not to see it. In real airplanes it is obvious when you start a roll and look at the rudder ball, what shows if your turn is co-ordinated properly, Again, adverse yaw is when you initiate a bank, the down aileron induces drag and the nose of the plane goes in the opposite direction of the turn, that's why in REAL airplanes we use ruddder with the turn, left rudder with left aileron, but is is a momentary issue because when we get to desired bank, we take the aileron input out, back to neutral and maintain the turn and altitude with elevator. That's why we don't notice it in our models because it is very quick.