The Sword of Sealing was a form that the Light of Hope took to help Sailor Moon defeat Sailor Galaxia in the anime. It was a large sword, with a wide blade and two red gems set into the hilt.
Sailor Moon refused to use the sword to fight Sailor Galaxia, and it shattered when Sailor Galaxia struck it with her own blade. The sword then reverted to the form of Sailor Chibi Chibi Moon before disappearing.
Sailor Galaxia used a similar sword in order to seal Chaos within her own body. While under the influence of Chaos, Galaxia used a darker version of that sword to battle the Sailor Starlights. When Galaxia was totally consumed by Chaos, she used the sword to fight Princess Serenity and shatter the Sword of Sealing.