I/O Classes, or Input/Output Classes, are essential components in programming that manage the flow of data between a program and external sources, such as files or user interfaces. They help developers read data from input devices, like keyboards, and write data to output devices, such as screens or printers. In many programming languages, like Java or Python, I/O Classes provide built-in methods to simplify these tasks. For example, FileReader and FileWriter in Java allow easy manipulation of files, while open() and read() functions in Python facilitate file handling, making data management more efficient.