The Affective Filter Hypothesis is a theory in second language acquisition proposed by linguist Stephen Krashen. It suggests that emotional factors, such as anxiety, motivation, and self-confidence, can influence a learner's ability to acquire a new language. When learners experience negative emotions, their "affective filter" rises, blocking input and hindering language learning. Conversely, when learners feel relaxed and motivated, their affective filter lowers, allowing for better absorption of language input. This hypothesis emphasizes the importance of creating a supportive and positive learning environment to facilitate effective language acquisition.