Deimos (or Mars II) comes from the Greek word for terror. It is the smaller moon of Mars. Phobos is the other moon of Mars, which is larger than Deimos.
Deimos is only 15 kilometers in diameter. It is covered with craters, as Earth's moon is.
It is named after the god Deimos in Greek mythology, who was one of Mars' sons, and means Panic.
The other moon, Phobos, is the larger of the two.