An ES Module (ESM) is the modern standard for organizing and sharing JavaScript code. Introduced in ECMAScript 2015 (ES6), ESM allows developers to split code into reusable files using 'import' and 'export' statements. This modular approach improves code maintainability, reusability, and security by enabling strict scoping and isolation of variables. ESM supports asynchronous loading, which can enhance web application performance by loading only the necessary modules when needed. Unlike older module systems like CommonJS, ESM is natively supported in browsers and Node.js, making it a versatile choice for both client-side and server-side JavaScript development. ESM also helps prevent common security risks, such as variable leakage and unintended global scope modifications, by enforcing strict module boundaries.