Siri is a virtual assistant developed by Apple that uses voice recognition to perform tasks and answer questions. It is integrated into various Apple devices, including the iPhone, iPad, and Mac, allowing users to interact with their devices hands-free. With Siri, users can send messages, set reminders, play music, and access information from the web. The assistant continually learns from user interactions, improving its responses and capabilities over time, making it a valuable tool for enhancing productivity and convenience in daily life.