ECMAScript 2015, also known as ES6, is a significant update to the JavaScript programming language. It introduced new features that enhance the language's capabilities, making it easier for developers to write complex applications. Key additions include arrow functions, classes, and modules, which help organize code better and improve readability. This version also brought improvements to existing features, such as promises for better handling of asynchronous operations and template literals for easier string manipulation. Overall, ECMAScript 2015 marked a major step forward in modernizing JavaScript, making it more powerful and user-friendly for developers.