The Lord of the Rings spinoff game with the “Gravewalker” title is Middle-earth: Shadow of Mordor. The term appears in the game’s 2014 “Gravewalker” trailer and related materials for that game.

What it refers to

“Gravewalker” is strongly associated with Talion , the main character in Shadow of Mordor , and it also shows up as a rune/item name in that game’s ecosystem.

Related game

  • Middle-earth: Shadow of Mordor — the original game tied to the Gravewalker name.
  • Middle-earth: Shadow of War — the sequel, where the term still appears in community discussion and content, but it is not the original source of the name.

TL;DR: It was Middle-earth: Shadow of Mordor.