C11, or C11 language, is a version of the C programming language standardized in 2011. It introduced several new features aimed at improving performance, safety, and ease of use for developers. Key enhancements include support for multithreading, lambda expressions, and improved type inference. Additionally, C11 added new library functions and improved support for Unicode, making it easier to work with international text. The standard also emphasizes better compatibility with modern hardware, allowing developers to write more efficient and portable code across different platforms.