The Elvish prefix Mor means Black but there are many places it is used. Here are some of them.Moria
In The Lord of the Rings this meant Black Pit; another time it meant Black Gulf.Morgul (at one point Morgol)
This name can be seen in e.g. Minas Morgul which was what was once Minas Ithil but after being captured by the Nazgûl it was the Tower of (Black) Sorcery (though it had other names).Morgai
Sam encounters this just as he enters Mordor. On pg. 899 of the 50th anniversary edition of The Lord of the Rings (HarperCollins Publisher) it's described like this:
Hard and cruel and bitter was the land that met his gaze. Before his feet the highest ridge of the Ephel Dúath fell steeply in great cliffs down into a dark trough, on the further side of which there rose another ridge, much lower, its edge notched and jagged with crags like fangs that stood out black against the red light behind them: it was the grim Morgai, the inner ring of the fences of the land. Far beyond it, but almost straight ahead, across a wide lake of darkness dotted with tiny fires, there was a great burning glow; and from it rose in huge columns a swirling smoke, dusty red at the roots, black above where it merged into the billowing canopy that roofed in all the accursed land.
Sam was looking at Orodruin, the Mountain of Fire. [...]
Earlier known as Melkor ('He Who Arises in Might'), at that point mightiest of the Valar, Fëanor named him Morgoth after he colluded with Ungoliant(e) to darken the world and then steal the Silmarils (and other jewels but it was the Silmarils that were most coveted): Black Enemy, Black Foe; and no longer was he considered part of the Valar.Morannon
This was the Black Gate of Mordor (Black Land, see next section): this was where Frodo with Gollum and his servant Sam first went but because it was closed Gollum would lead them to the other way; they would be captured by Faramir Captain of Gondor and they would be released and then Gollum would lead them on towards Mordor.