Writer is the superclass of all character output streams.
One of the early inventions of the UNIX operating system was the pipe. By unifying disparate ways of communicating into a single metaphor, UNIX paved the way for a whole series of related inventions, culminating in the abstraction known as streams. A pipe is an uninterpreted stream of bytes that can be used for communicating between programs or for reading and writing to peripheral devices and files. A stream is a path of communication between the source of some information and its destination. In fact, the source and destination of the information are completely arbitrary producers and consumers of bytes.