Secunda

 is the smaller of the two moons in the orbit of Nirn, the other being Masser. If the player looks up at the sky at night they can easily be seen, but strangely in it's noticeable that Secunda actually revolves around Masser, so in a sense Secunda is Masser's moon. These two moons don't really contribute anything to gameplay in Elder Scrolls games except for the fact that Secunda becomes the Bloodmoon (turning red) in expansion of Morrowind.

Trivia

 * Secunda is in a very unstable orbit both due to the close proximity of Nirn and the fact that it is being "tugged" on by both Nirn and Masser that suggests it may eventually plummet into Nirn or be thrown into space.
 * In the real world a "moon of a moon" would only be able to orbit the parent moon for a relatively short period of time before losing orbit and being sucked into the larger moon.
 * The giant camp Secunda's Kiss in Skyrim is most likely named after the moon.
 * Secunda is the name of a song in the Skyrim Official Soundtrack.