A swift reaction refers to a prompt and immediate response or action in response to something. It is characterized by speed, efficiency, and quick thinking, as someone who has a swift reaction is able to respond quickly to a situation without hesitation. The term can be used both positively and negatively - for example, it could refer to a person's ability to react quickly in an emergency or crisis, but also to their impulsive behavior that may not always be beneficial. Overall, the phrase "swift reaction" highlights the importance of being able to respond effectively and efficiently in real-time situations.