An Input Stream is a sequence of data that is read from a source, such as a file, network connection, or keyboard. It allows programs to receive data in a structured way, enabling them to process information efficiently. Input streams can handle various data types, including text and binary data, making them versatile for different applications. In programming, input streams are often used in conjunction with output streams to facilitate data transfer. For example, in the Java programming language, the InputStream class provides methods to read bytes from a source, while the OutputStream class allows writing data to a destination.