Can someone explain the -t option/flag in docker run command?

I know that -t flag is used along with -i flag for getting an interactive shell. But I cannot digest what the man page for docker run command says about this flag, which is the following,

       -t, --tty=true|false
          Allocate a pseudo-TTY. The default is false.

       When set to true Docker can allocate a pseudo-tty and attach to the standard input of
       any container. This can be used, for example, to run a throwaway interactive shell.
       The default is false.

       The -t option is incompatible with a redirection of the docker client standard input.

Things like pseudo-TTY or “attaching to the standard input”. So if this interactive shell isn’t the standard input for docker container, what is actually the standard input, to which it attaches?