Title: Imperator

What is the Title, Imperator?

I found it on Karsh advanced, but it is nowhere in the rulebook.

Is it a sect title? If so, then which sect?

There is a political card called the same.

Imperator

Title.Choose a Camarilla vampire with capacity 8 or more. Successful referendum means this card is put on the chosen vampire to represent the unique Camarilla title of Imperator (worth 3 votes). This vampire can play cards named Blood Hunt from your hand or ash heap as a prince. This vampire gets +3 votes in blood hunt referendums.

I would assume it's at least a +3 vote unique camarilla title.

The additional effects - blood hunt refs and playing Blood Hunt card, Karsh (adv) has these already.

(I cannot find any specific ruling.)

Good catch, Norm.