Each of the 19 buffers has a name, usually derived from the name of the file it comes from. This commands allows you to redefine the name of the current buffer.
Just as when you save data, when you give a new name for a buffer,
!! is a shortcut for the current name. E.g. if you buffer is
dummy.dat, and if you type
!!X after the prompt
New name ([abort]) :, the data set will be renamed