Complex sentence: Cross-site scripting (XSS) is a type of computer security vulnerability typically found in Web applications, accesed through web browsers through breaches of browser security, that enables attackers to inject client-side script into Web pages viewed by other users.
Split into simpler sentences: Cross-site scripting (XSS) is a type of computer security vulnerability typically found in Web applications, generally accesed through web browsers. Through breaches of browser security, XSS enables attackers to inject client-side script into Web pages viewed by other users.