Watch the Single String Studies Pt. 2 online guitar lesson by Brad Carlton from Guitar Lab: Precision Strumming

Rest strokes are defined as a pick or finger stroke which contacts not only the string being played, but also comes to rest against the next highest pitch sting when using a downstroke with the thumb or the pick, and in the case of an upstroke with a finger or the pick, you come to rest against the next lowest pitched string. Rest strokes should be viewed as a follow-through of the pick or finger stroke.