Mithral
Mithral is one of several magical metals from the settings of Dungeons & Dragons, and is one of the two most iconic, after Adamantine. Characterized by its beautiful bright silvery color, mithral is notable for having high durability whilst being lightweight; weapons made from mithral may not have the innate cutting power of adamantine weapons, but armor made from mithral is exceedingly light and easy to move in, whilst still offering better protection than anything made of steel.
Mithral originates from the writings of J.R.R. Tolkien, who envisioned this ultra-durable, silver-like metal as the most precious and valuable ore on Middle-Earth. He spelled his version as Mithril, whilst D&D changed the i to an a in order to avoid copyright. Still, the two names sound so alike that they are generally used interchangeably, especially as their effects are identical. It might just be Titanium as it has basically all the qualities of Titanium, even appearance.
While Mithril in Middle-Earth is exceedingly rare, in the higher fantasy settings of D&D Mithral is merely rare. It's obtainable to the point where it's a standard part of many builds. Mithral armor is extremely desirable in 3.5 because it counts as one weight class lighter, with heavy armor being treated as medium and medium armor being treated as light. This makes mithral the ideal material for classes locked into light or medium armor. Mithral bucklers are particularly desirable, as they're the only type of shield in the game that naturally has no spell failure chance, making them a point of AC at a fair cost that can't be gotten any other way for just about any spellcaster.