Cirith Ungol in Sindarin means 'pass of the spider'.
From J.R.R. Tolkien's The Lord of the Rings, it is a pass over the Ephel Duath, just north of Minas Morgul, and guarded by the Tower of Cirith Ungol. It was used by the Nazgûl in TA 2000 when those nine servants of Sauron rode forth to attack the men at Minas Ithil. Frodo and Samwise also used this pass in their quest in Mordor. It was heavily guarded by Orcs and other dark creatures, however it was easier to pass this way undetected than to take the main route, which was behind Minas Ithil.
Though Cirith Ungol itself was just the road East of Shelob's lair, it was also used to refer to the entire area from Imlad Morgul to the Morgai. It was also called the High Pass by Sam.