microdots

/M AY1 K R OW0 D AA0 T S/
noun
  1. 1

    A text or photographic image that has been reduced in size to that of a typographical dot in order to escape detection by unintended recipients.

  2. 2

    A small-sized tablet containing lysergic acid diethylamide (LSD).

Source: https://en.wiktionary.org/wiki/microdot, https://en.wiktionary.org/wiki/microdots