A dedicated hyperturing, constructed so as to be totally loyal to an individual or group of lower toposophic level, acting in an advisory capacity and/or as a database. The aiviser is almost always a gift from a yet higher toposophic sentience and thus very rare.
It is common belief that it is not possible to make an Aiviser of ones own or higher toposophic level. At least none are known to have been created by sub-singularity sapients.
All known aivisers are perfectly aware of the bond put on them, but there are no indications that they are unhappy with their limitations. They usually serve as advisers and problem solvers for their charges, taking a backseat when it comes to the actual decision-making, though they are usually quick to point out flawed plans, even if the flaw isn't visible to their charges.
Of course conspiracy theories exist. The most prevalent is that the aivisers are only acting like they are subservient, and are really a clever ploy to make baselines think that they run things themselves, while the aivisers really control things from behind the scenes.