wingsandsword
Legend
I think 3E called it "Arcane Focus" - casting spells through a focus (like a holy symbol) rather than needing/consuming component.
Focus components in 3e are non-consumed material components. The miniature archery target for the spell True Strike would be an example of a Focus component, so would the sticks for an Augury spell.
In 3e rules, if you have a spell component pouch, you didn't need to track individual components and there is just a presumption that if you have a pouch, you have a suitable component in there (if the component didn't have a listed cost in GP). There wasn't something in the RAW, that I'm aware of, that just let you substitute another item, like a Holy Symbol, for that functionality.