Material component

One or more physical substances or objects that are annihilated by the spell energies in the casting process. In DDO, all the spells of the same level and class which require a material component use the same item. Those items are sold by "Reagent" vendors around Stormreach. They stack together, so a typical spellcaster will keep hundreds of components on hand for each of the spell levels he can cast (even though for some classes, like cleric, the spells which do need components are some of the less often used).

The Stoneskin arcane spell is a special case, as it requires a separate kind of material component which is more expensive than the others.

Spell components can sometimes be found as treasure in DDO, and interestingly this includes components for 6th level spells, which no PC in the game's level cap can use.