Node.js is an open-source, cross-platform runtime environment that executes JavaScript code on the server side. It provides a rich set of libraries and modules, making it ideal for building scalable and high-performance web applications. With Node.js, developers can leverage JavaScript's asynchronous and event-driven nature to create efficient and real-time applications.

REPL stands for "Read-Eval-Print Loop." It is an interactive programming environment that allows you to enter and execute code snippets in real time. With a REPL, you can enter code, have it evaluated, and see the results immediately. It is commonly used for experimenting with code, testing small code snippets, and learning programming languages. Node.js provides a built-in REPL environment where you can interactively execute JavaScript code and see the output instantly.