I believe it means "craddle of life" in some ancient language.
That's what it's called by the inhabitants of Toril at least. A little known fact though is that the human and elven inhabitants of the moon themselves call their world "Leira", the name of the now deceased Forgotten Realms goddess of illusion and trickery. Long story there. The "Tears of Selune" are a cluster of asteroids.
They are, in order, out from the sun:
• Anadia (Sperical earth planet with Umber Hulks and polar halflings inhabitants)
• Coliar (Spherical gas planet w/ floating earth islands, aarakocra and lizardmen inhabitants)
• Abeir-Toril (Spherical earth planet)
• Karpri (Spherical water planet inhabited by aquatic elves and giant insects)
• Chandos (Spherical water planet inhabited by humans, dwarves and orcs)
• Glyth (Spherical earth planet w/ rings with mind flayer and humanoid slave inhabitants)
• Garden (A cluster of asteroids held together by a huge living plant called Yggdrasil's child)
• H'Catha (A flat water world with a single mountain on both sides; inhabited by beholders)
Asside from those celestial bodies, some of the planets have their own moons, most notably Garden which has twelve of its own (including it's own mini-sun/moon), a few comets, a handful of artificial satellites and some nebulae. Elminster also keeps a secret hideout at Coliar's core which houses his portals to his tower in Shadowdale, to the Island of Evermeet, to Yellowstone National park in the year 1894, a portal to Ed Greenwood's study in Ontario Canada in the present day as well as his closet full of gems and his stash of german beer. (I kid you not. Could I make this stuff up?!?)