Stderr stands for "standard error," which is a stream used in computing to output error messages and diagnostics from programs. It is one of the three standard streams in a computer system, alongside Stdout (standard output) and Stdin (standard input). By default, Stderr displays messages on the screen, helping users identify issues during program execution. Unlike Stdout, which is used for regular output, Stderr is typically unbuffered. This means that error messages appear immediately, allowing for quicker troubleshooting. Developers often redirect Stderr to log files or other outputs to separate error messages from standard output, making it easier to analyze problems.