The FS (File System) module is a built-in module in Node.js that provides an API for interacting with the file system. This module allows developers to perform various file operations such as reading, writing, updating, deleting, and renaming files.

One of the most commonly used methods in the FS module is the fs.readFile() method, which reads the content of a file asynchronously and returns its content in a callback function. Another popular method is fs.writeFile(), which writes data to a file asynchronously.

Other frequently used methods include:

• fs.mkdir() to create a new directory
• fs.readdir() to read the contents of a directory
• fs.stat() to get information about a file
• fs.unlink() to delete a file
• fs.rename() to rename a file

The FS module also provides synchronous versions of these methods, which can be useful for simple scripts or small applications where performance is not a major concern. However, it's generally recommended to use the asynchronous versions of these methods, as they are non-blocking and allow for better performance in larger applications.

Overall, the FS module is a powerful tool for developers working with Node.js, as it enables them to easily interact with the file system and perform a wide range of file operations.