Named after Deimos (terror and dread) who accompanied their father Ares (Mars in Roman mythology, hence the name of the planet) into battle.
Deimos measures 12.6 km (7.8 mi) across, with a mass of 1.5×1015 kg.
Deimos is tidally locked, always presenting the same face towards Mars.
Deimos orbits farther than Phobos with a semi-major axis of 23,460 km (14,580 mi) and an orbital period of 30.35 hours.
Deimos would look more like a bright star or planet (only slightly bigger than how Venus looks from Earth) for an observer on Mars. It has an angular diameter of about 2'.
Deimos, is far enough away that its orbit is being slowly boosted instead, akin to Earth's Moon.