Form validation is a process used in web development to ensure that the data entered by users into a form meets specific criteria before it is submitted. This helps prevent errors and ensures that the information collected is accurate and complete. Common validation checks include verifying that required fields are filled out, email addresses are in the correct format, and passwords meet security standards. There are two main types of form validation: client-side and server-side. Client-side validation occurs in the user's browser, providing immediate feedback, while server-side validation happens on the server after the form is submitted. Both methods work together to enhance user experience and data integrity.