What is Cross site scripting :-
As quoted in wiky
"Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications that enables malicious attackers to inject client-side script into web pages viewed by other users. An exploited cross-site scripting vulnerability can be used by attackers to bypass access controls such as the same origin policy. Cross-site scripting carried out on websites were roughly 80% of all security vulnerabilities documented by Symantec as of 2007. Their impact may range from a petty nuisance to a significant security risk, depending on the sensitivity of the data handled by the vulnerable site, and the nature of any security mitigations implemented by the site's owner."
There is no single, standardized classification of cross-site scripting flaws. but most
experts distinguish between at least two primary flavors of XSS non-persistent
and persistent to know whats persistent and non persistent click here