Final answer:
Solitary play and onlooker play are stages of play in child development that represent different levels of social interaction, with solitary being alone and onlooker involving watching but not participating.
Step-by-step explanation:
Solitary play and onlooker play can both be categorized as stages of play in child development. Solitary play refers to when a child plays alone, focusing on their activity without seeking interaction with others.
Conversely, onlooker play occurs when a child watches others play but does not participate directly; they observe and may engage in social interaction without joining the activity.
These stages are identified within educational psychology and are part of understanding how children interact and relate to their environment as they grow.