This article reviews the proliferation of terms that have been coined to denote the language environment of the young child. It is argued that terms are often deployed by researchers without due consideration of their appropriateness for particular empirical studies. It is further suggested that just three of the dozen or more available terms meet the needs of child language researchers in most instances: "child-directed speech," "infant-directed speech" and "exposure language." The phenomena denoted by these terms are then considered. The term register is generally borrowed for this purpose from sociolinguistics. However, close inspection of this concept reveals that the notion of register needs to be constrained, in specified ways, in order to be of any real value within the field of child language research.