What does the 'SUD' message mean on my washer display?

'SUD' indicates that excessive suds have been detected and a suds routine has automatically started to remove extra suds and ensure proper rinsing of garments. This message displays during rinsing and at the end of the cycle to inform you the Suds Routine was activated. To prevent this, use only HE (High Efficiency) detergents in the correct amounts. (Page 19)