The Ear was a secret shadowy agency within the Ferengi Alliance that was tasked with doing covert operations. It was considered similar to the Cardassian Obsidian Order, Romulan Tal Shiar and Human Section 31. They were based in the lowest hall in the Nagul Palace on Ferenginar.
They were considered a dead clan of Ferengi that were trained in the arts of covert operations, secrecy and surveillance. Their nature within the nagul government meant that their existence was hidden though Grand Nagus Zek knew of them but had forgotten to tell his successor, Rom. Only a few were capable of finding their existence and even fewer managed to survive after learning of their presence. (DS9 short story: "The Last Tree on Ferenginar: A Ferengi Fable From the Future")