Silver

Silver, Alchemical: A complex process involving metallurgy and alchemy can bond silver to a weapon made of steel so that it bypasses the protective damage reduction of creatures such as devils and vampires.

Silver weapons have 2 points lower hardness then equivalent steel weapons, and as such aren't quite as durable. Silver weapons can bypass the damage reductions of Vampires and of most Devils. With some devils, Good-typed damage (via Holy, Holy Burst, Pure Good, Righteousness, or Aligned modifiers) may be needed in addition (Pit Fiends like Arraetrikos) or instead (Bezekira). Note that Succubi are typed as Devils, but have DR/Cold Iron or Good like Demons instead.

DDO doesn't have any Lycanthrope monster as of Update 10.

Monks with the Shintao Monk III enhancement can bypass Silver damage reduction with unarmed attacks.

Bows "made of silver" do not bypass Silver DR on foes. Any bows loaded with silver ammo do bypass Silver DR however. Metalline bows, however, do bypass any metal-based DR, regardless of the ammo.

History
In the original release of DDO, silver weapons worked more like their pen and paper counterparts and dealt 1 point less damage per swing. This was changed to simplify the game.