Spring Security is a powerful and highly customizable authentication and access-control framework. It provides comprehensive security services for Java applications, especially those using Spring. It integrates with Spring MVC and offers a variety of authentication mechanisms, such as form-based login, HTTP Basic, JWT, OAuth2, and more. Spring Security also supports authorization at both the URL level and the method level. It's essential for developers to understand how to properly configure Spring Security to ensure the security of their applications.