This is not an official term.
Vezon followed Tridax through hallways into a sub-basement. At the bottom of the basement was a massive chamber. The walls towered 40 feet all around. Lining them were close to 100 stasis tubes, each one occupied by an identical figure: Toa Takanuva. A few of them had armor of jet black, and most of them were white and gold. Tridax considered this the most powerful secret of Destral. The development of the shadow leech sparked an idea in Tridax. Tridax used a Kanohi Olmak, one of only two known to exist, to visit other realities. He collected the Toa Takanuva of each, bringing them back to the chamber and their light to his shadow leeches. His goal was to make an army of shadow Toa, all made from the most dangerous enemy of the Makuta. The Toa were kept asleep inside crystalline cases.
One of the dark Takanuvas had all black armor. He also inexplicably had a desire to destroy the world. After the attack on Destral, some of the Takanuva duplicates were dead, and some were still trapped in suspended animation.