What is "shelob"

Shelob is a fictional giant spider from J. R. R. Tolkien's Middle-earth legendarium. She appears at the end of the fourth book, second volume ( The Two Towers), of The Lord of the Rings. Her lair lies in Cirith Ungol ("the pass of the spider") leading into Mordor. Gollum deliberately leads Frodo Baggins there in hopes of recovering the One Ring when Shelob attacks Frodo. The plan is foiled when Samwise Gamgee greatly injures Shelob with Frodo's Elvish dagger, Sting, and the Phial of Galadriel.