XSS (Cross-Site Scripting) is a type of security vulnerability that can be found in web
applications. It allows an attacker to inject malicious code, such as scripts, into a web page
viewed by other users. This can lead to the theft of sensitive information, such as login
credentials or personal data, and can also be used to hijack user sessions or redirect users to
malicious websites. The severity of an XSS vulnerability can range from minor annoyance to
significant risk to the security of a web application and its users.