Spyware is a type of malicious software designed to secretly monitor and collect information from a user's device without their consent. It can track activities such as browsing habits, keystrokes, and personal data, often sending this information to third parties. This software can be installed through deceptive methods, like bundled software downloads or phishing emails. Once on a device, spyware can compromise privacy and security, making it important for users to have protective measures, such as antivirus programs, to detect and remove it.