Reflected Cross-Site Scripting (XSS) is a type of security vulnerability found in web applications. It occurs when an attacker sends a malicious script to a website, which then reflects that script back to the user's browser without proper validation. This can happen through URLs or form inputs, allowing the attacker to execute harmful code in the context of the victim's session. When a user clicks on a link containing the malicious script, their browser runs it as if it came from a trusted source. This can lead to unauthorized actions, such as stealing cookies or sensitive information. To protect against Reflected XSS, developers should validate and sanitize user inputs effectively.