Silvermoon Remnant

The Silvermoon Remnant was a planned reputation faction which included certain high elves found in game, but not all of them. The term has received only a single reference in the patch 1.6 notes, and nowhere else.

"High Elves now have their own distinct faction -- 'Silvermoon Remnant'. This faction is allied with the Alliance and is at war with the Horde. Not all High Elves are a part of this faction."

Beyond the single reference to the faction in the patch notes, no references appear in game, and there is no knowledge as to what particular high elves belonged to it. Nor is there any information regarding whether Blizzard still considers it an official group. Unlike other non-rep factions like Earthen Ring no references to this group were ever made in game, and no high elves have the title.

The Silver Covenant was probably inspired by this faction as a beacon for high elves in the Alliance.

Speculation
Some assume that they were going to be the remnants of the high elves that remained loyal to the Alliance and followed Jaina Proudmoore to Kalimdor. Those high elves traveled across the Great Sea with Jaina and helped her build the island city of Theramore. Others believe it would have included the high elves seen in Hinterlands, Plaguelands, and other Eastern Kingdom areas where they are seen in larger numbers.