What is the term for an infant's expression of concern upon seeing a stranger?

The correct term for an infant's expression of concern upon seeing a stranger is "Stranger wariness." This phenomenon typically emerges in infants around 6 to 12 months of age and is characterized by hesitation, anxiety, or fear when encountering unfamiliar individuals. It is a normal developmental milestone that reflects an infant's growing cognitive abilities and social awareness.

Stranger wariness signifies that the infant has developed some sense of attachment to their primary caregivers and is beginning to differentiate familiar people from those who are not part of their everyday experience. As infants grow older, this wariness can help them learn to navigate social situations and develop a sense of safety and security.

Other terms, such as "goodness of fit," refer to the compatibility between a child's temperament and their environment, rather than a specific emotional response to strangers. "Separation anxiety" involves distress when a caregiver leaves, while "synchrony" pertains to the coordinated interactions between a caregiver and a child, neither of which specifically describes the reaction to unfamiliar people.