The term "functional play" is used widely and variably in serving young children who have developmental delays, affecting its use in research and practice. It also is confused with play as a functional goal. We reviewed studies that used the term. Of 146 reports, less than half included a definition. We organized those with definitions into two groups: one in terms of appropriate use of toys and the other in terms of motor activities. We conclude that the toy-directed focus subsumed in appropriate use is subject to wide variation in interpretation, and it should not be used as a category of play. It does not explicitly take into account children's developmental progress in play. We recommend the term should be reserved for activities that support engagement and interest. Such activities represent play as functional for a child, requiring an understanding of children's progress in play, which is play that is child-focused.