I/O stands for input and output. It accesses anything outside of your application. It loaded into the machine memory to run the program, once the application starts.

In the context of Node.js, I/O (Input/Output) refers to the processes of reading and writing data to and from external sources such as files, networks, or databases. In Node.js, I/O operations are non-blocking, meaning that while one operation is in progress, the program can continue executing other tasks without waiting for the I/O operation to complete. This is facilitated by asynchronous programming patterns and the event-driven architecture of Node.js, which allows for efficient handling of I/O operations without blocking the execution of other code.