(
CROSS-Site 
Scripting)  Causing a user's Web browser to execute a malicious script.  There are several ways this is done.  One approach is to hide code in a "click here" hyperlink attached to a URL that points to a non-existent Web page.  When the page is not found, the script is returned with the bogus URL, and the user's browser executes it.
An "XSS hole" is a vulnerability in an application that enables cross-site scripting to be exploited.  See 
parameter tampering, 
buffer overflow and 
CSRF.