Noble Phantasm

The armaments carried by Heroic Spirits, made from humanity's illusions.
Though they generally come in the form of things like swords, spears, or bows, there are also those Heroic Spirits whose Noble Phantasms are auxiliary armaments like shields, rings, or crowns.
They are solidified “mysteries,” and injecting them with magical energy while calling their true name will unleash their abilities.

Fate/side material: Fate Encyclopedia