I am following a guide to learn terminal commands and have encountered the use of hyphens to refer to stdin in the following command used to find all files named 'file-A' within the directory playground. I understand it's usage to refer to the files found by the find command which are of course piped to tar and set to be read as a file using the --files-from= option. I do not understand it's usage in defining the intermediary name of the archive before being renamed by the gzip command.
find ./playground -name 'file-A' | tar -cf - --files-from=- | gzip playground.tgz
Would the value of stdin not be a list of paths defined in the stdin file? if so how can this be an acceptable name for the archive?