File I/O in Java refers to the process of reading from and writing to files using the Java I/O API. This functionality is essential for data manipulation in applications, allowing developers to handle various file types efficiently. Java provides two primary categories of streams for file operations: byte streams (InputStream/OutputStream) for raw binary data and character streams (Reader/Writer) for character data, which supports internationalization. The java.io package contains the necessary classes for these operations, making it a fundamental aspect of Java programming for tasks ranging from simple file handling to complex data processing in applications.