A ring of spell storing was a magical ring that could trap Spells cast inside of it, holding the magic until an attuned wearer chose to release them. Any creature, regardless of magical ability, could cast spells by touching the ring, and the spell would come out with the potency put in by the original spellcaster. These devices were made as convenience for wizards and other arcane casters, but occasionally resulted in disaster if they fell into the wrong hands.
Most rings could hold a small amount of minor magic, but occasionally, rings of higher "bandwidth" were created, allowing for greater magical effects to be stored indefinitely.