The Orb of power is the essence/power released from an Another's body after that another dies or is killed. Its size varies proportionately to the level of Another; i.e. the higher the level of the Another, the bigger the orb gets. It can only be absorbed by other Anothers. The only exception to this is Yu-Hwa who despite being a human, absorbed an orb.
An orb contains about 10% power of the dead Another it is created from. However, not all of that power can be imbibed by the one who absorbs it. The stronger the Another blood, the more power one can absorb from the orb.
Throughout the series many Anothers kill others of their kin for increasing their own power.
Han Yu-Hwa accidentally absorbed Lecter's power orb when Sa-Ryun and Mase were fighting each other for it. It can be only absorbed by those with Another blood so this development surprised everyone as Yu-Hwa is a human. It has been speculated that the Crystal within Yu-Hwa helped him to absorb this power orb.