GRaphical INterpretive Display.
1. (MIT and Berkeley) To prettify hardcopy of code, especially LISP code, by reindenting lines, printing keywords and comments in distinct fonts (if available), etc. This usage was associated with the MacLISP community and is now rare; prettyprint was and is the generic term for such operations.
2. (Unix) To generate the formatted version of a document from the nroff, troff, TeX, or Scribe source.
3. To run seemingly interminably, especially (but not necessarily) if performing some tedious and inherently useless task. Similar to crunch or grovel. Grinding has a connotation of using a lot of CPU time, but it is possible to grind a disk, network, etc.
See also hog.
4. To make the whole system slow. "Troff really grinds a PDP-11."
5. "grind grind" excl. Roughly, "Isn't the machine slow today!"