What does "Cross-Site Scripting" (XSS) refer to?

Cross-Site Scripting (XSS) refers to a type of security vulnerability that enables an attacker to inject malicious scripts into web pages that other users view. This typically occurs when a web application does not correctly validate or encode user input, allowing the attacker to execute arbitrary JavaScript in the context of another user's browser. The consequences can range from stealing session cookies, recording keystrokes, defacing web pages, to redirecting the user to malicious sites, posing serious risks to user security and privacy.

Understanding XSS is crucial in secure software design because it highlights the importance of input validation and output encoding. By addressing these vulnerabilities, developers can safeguard against attackers who exploit these weaknesses to execute harmful scripts, preserving the integrity and security of web applications.

The other options provided do not accurately represent XSS. The second choice speaks to general security enhancements for web servers, which is unrelated to script injection. The third and fourth choices discuss optimization and user experience techniques, but neither relates to the malicious exploitation characteristic of Cross-Site Scripting.