What does the flag '-d' do in a 'docker run' command?

The flag '-d' in a 'docker run' command is used to run the container in detached mode. When a container is started in detached mode, it runs in the background, allowing the command prompt or terminal to be freed up for other tasks. This is particularly useful when you want your application or service to continue running without being tied to the terminal session, which is common in production scenarios or when automating deployment pipelines.

Running a container in detached mode is essential for scenarios where you need to manage multiple containers simultaneously or need to keep services running continuously without direct interaction. The output from the container does not appear in the terminal; instead, you can monitor logs and status using separate Docker commands, such as 'docker logs' or 'docker ps'. This option provides flexibility in managing long-running processes without cluttering the terminal with output.