Final answer:
stdin, stdout, and stderr refer to the three default file descriptors in Unix-like operating systems. stdin corresponds to the keyboard input with file descriptor 0, stdout to the screen output with file descriptor 1, and stderr to the error messages with file descriptor 2.
Step-by-step explanation:
stdin, stdout, and stderr are the three default file descriptors in Unix-like operating systems. stdin (standard input) is the default input channel and is typically associated with keyboard input. Its file descriptor number is 0.
stdout (standard output) is the default output channel, usually displayed on the screen, and has the file descriptor of 1. stderr (standard error) is used for error messages and diagnostics; it is also displayed on the screen and has the file descriptor of 2. These default file descriptors are utilized by the system for managing inputs and outputs in a consistent way.