Critical periods are times in an organism's development when they are particularly sensitive to certain stimuli or experiences. Synonyms for critical periods include sensitive periods, developmental windows, crucial phases, and important stages. Sensitive periods refer specifically to when an organism is particularly responsive to a given stimulus, such as language or social interaction. Developmental windows suggest a period of opportunity that is open for a limited time. Crucial phases highlight the importance of specific stages in an organism's development. Important stages emphasize the significance of particular periods during which certain experiences or exposures can have a strong impact on an organism's long-term outcomes. Understanding critical periods is essential for optimizing human and animal development.