A Spellcasting Focus was a basic tool employed in Spellcraft. Though there was no consistent idea on what made a good focus, it was generally an item of magically conducive material or one that had personal significance to the caster.
Arcane focuses were usually small enough to store in a spell component pouch and were very cheap; however, unlike many other types of material Spell Components, arcane focuses were not consumed by the casting of the spell and could be reused. Many were crafted from gems, jewelry, wands, or other easy-to-store objects.
A divine type of arcane focus was referred to a "holy symbol." They often came in the form of amulets, emblems on shields, or reliquaries that contained fragments of sacred material. Like other arcane focuses, holy symbols were cheap to produce and not necessarily inherently magical. Despite this, they were thought to be blessed directly by divine or powerful beings, and often depicted representations of their religions.