The Orb is one the greatest artifacts of the Dragaeran Empire.
The Orb circles the head of the current Emperor, and all citizens of the Empire (including those who have bought titles, or who have sworn loyalty) have a link to it that allows, among other things, Sorcery.
The Orb was initially created from trellanstone by Zerika the First, who along with Kieron founded the Empire from the initial tribes (which later became Houses). It became the medium for controlling power from the Greater Sea of Chaos, as well as its protection against the Jenoine.
It was fashioned using Elder Sorcery, but its creation led to the banning of Elder Sorcery, due to the dangers involved. (Presumably, Elder Sorcery was also banned in part to prevent any rogue Elder Sorcerers from challenging the Orb itself — see Adron's Disaster.)
During Adron's Disaster, Sethra Lavode was able to save the Orb by sending it to the Paths of the Dead. During its time among the gods, the Orb was 'improved' or 'purified and enhanced' allowing much stronger sorcery, upon its recovery by Zerika the Fourth, than prior to the Interregnum.
Attributes & Abilities
Physically, the Orb is a multi-faceted sphere with a diameter of about eight or nine inches. Its default color while inactive is a very dark grey. It weighs about ten or fifteen pounds. It is not entirely spherical, having many small faceted sides. (This leads to the expression "More (something) than the Orb has facets".)
The Orb is a repository of the collected knowledge of every emperor or empress who has ever worn it. This information is typically used to help the reigning ruler make wise (or at least informed) decisions.
The Orb also acts as a sort of universal clock, allowing any citizen of the Empire to get the exact time by "consulting the Orb" mentally. Its large databanks also allow any Emperor to make an accurate map of any part of the empire by consulting it. The Orb will attempt to defend the Emperor from physical or sorcerous attack, though it can be overloaded. Any Imperial citizen can also contact the Emperor at any time through their link to the Orb. This is generally not used, however, since messages of insufficient importance could lead to the immediate obliteration of the citizen in question.
Among its more minor functions, the Orb changes color according to the mood of the emperor.
The Orb can be used as a 'lie detector'; suspects can be questioned under it, or testify under it as witnesses. In this latter function, the Orb's 'literality' gives it a slight weakness -- Vlad Taltos was questioned under the Orb about the murder of Tagichatn, yet was able to avoid conviction despite being guilty (possibly because the questions were not asked in the right way). Vlad also testified under the Orb against the Jhereg in Phoenix. Khaavren was questioned under the Orb in The Phoenix Guards.