Event Detection is the process of identifying occurrences of specific activities, anomalies, or state changes within a data stream, such as sensor readings, video feeds, network traffic, or text. It is used across domains, including computer vision, natural language processing, cybersecurity, and fiber-optic sensing. Techniques range from threshold-based methods to machine learning models that classify or localize events in time and space, often in real time and under constraints of low latency or limited labeled data.