Short for Cross Site Scripting. A type of web based security vulnerability using client side scripts such as Javascript.
XSS takes place as a consequence of improper input sanitization. When the input provided by the user is not properly sanitized, an ill willed user
may insert scripting
code into a web page, which in turn will be executed by the visitor's browser. There are
2 kinds of XSS attacks: stored or reflected. Stored would
mean that the injected code is permanently stored in the page, such as in a comment. Reflected would
mean that it only appears once when the payload (i.e. the malicious input) is part of the request, maybe in parameters or cookies.