Client-Side Validation is a process used in web development to check user input before it is sent to the server. This validation occurs in the user's browser, ensuring that the data entered into forms meets specific criteria, such as correct formatting or required fields. By catching errors early, it enhances user experience and reduces unnecessary server load. Common techniques for Client-Side Validation include using JavaScript or HTML5 attributes like "required" and "pattern." While it improves usability, it is essential to remember that it should not replace Server-Side Validation, which provides a more secure and reliable way to handle data.