example:
vimdiff <(first command) <(second command)
the <() makes a file descriptor (/proc/self/fd/12, as example) and reads from here are simply the stdout of the subshell command in the chicken head.
It’s kind of an inverse tee:
stream_of_output | tee >(command_1) >(command_2)
there both command_1 and command_2 get the same stream of bits.