The farther moon of Mars.

Numbers (from Britannica.com)

  • Size: 9 x 7 x 7 miles
  • Orbit Radius: 14,545 mi.
  • Revolution: 30.3 hours

The word Deimos is from a Greek word 'δειμος' meaning fear or terror, just like Phobos, Mars's other moon. Phobos and Deimos, according to the writeup at Phobos, were the horses that pulled Mars/Ares' chariot.

(That just seems a little too convenient for moons that were only discovered in 1877, but that's only in hindsight. If Asaph Hall had discovered three moons on Mars instead of two, they'd likely have had different names entirely...)