Mordor: Land of fire and ash. Its black gates are guarded by more than just orcs. One does not simply walk into.
Silmaril: Three jewels forged by Feanor during the First Age. They were stolen my Morgoth.
Palantiri: Magical Objects that allowed long-distant communication.
Morgul Blade: Dagger used by the Nazgul. Victims stabbed by it will eventually turn into a wraith.
Barad Dur: Sauron's tower in Mordor.
Fell-beast: Dragon like creatures ridden by the Nazgul.
Maiar: The lesser of the Ainur. Sauron is a member of that race.
Nazgul: Once great kings of men, they were corrupted by Sauron and became wraiths. They are Sauron's most powerful servants.
They don't react well with water.
Sauron: Morgoth's most powerful servant. Forged the One Ring. He lost his physical form when the Ring was cut from his finger by Isildur, and was finally defeated when the Ring was destroyed during the War of the Ring.
Morgoth: Formerly known as Melkor and the most powerful of the Ainur. Stole the Silmarils and hid in his fortress, Angband before being defeated in the War of Wrath.
Morannon: The Black Gates of Mordor.
Three Rings for the Elven-kings under the sky,
Seven for the Dwarf-lords in their halls of stone,
Nine for Mortal Men doomed to die,
One for the Dark Lord on his dark throne
In the Land of Mordor where the Shadows lie.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the Land of Mordor where the Shadows lie.