Introduction to Tractate Horayot
Leviticus 4 discusses sacrifices that must be brought as a result of unintentional sins. Verses 1-12 discuss the unwitting sins of the high priest (the anointed priest) and verses 13-21 discuss the unwitting sins of the whole community of Israel. According to the rabbinic interpretation of these passages, they refer to a case where either the high priest or the sanhedrin (a court) permitted a certain action, which when performed unwittingly by an individual causes him to be liable to bring a sin-offering. In other words the court mistakenly permitted forbidden actions. Verses 1-12, according to the rabbis, refer to a case where the high priest himself performs the sin, and verses 13-21 refer to a case where the majority of the community performed the sin. In both cases a sacrificial bull must be brought, either by the high priest or by the sanhedrin. These bulls have different technical names which we will learn throughout the tractate.
The above is true with regard to all sins except accidental idol worship. If a court ruled that an action was not idol worship and the majority of the community performed the action, and later it was found that the court ruled wrongly, the court must bring a bull and a goat. This situation is referred to in Numbers 15:22-29. If an individual accidentally worshipped idols, he only brings a goat as a sin-offering. This situation is referred to in Numbers 15:27-29.
With regard to an individual accidentally worshipping idols, there is no distinction made between a high priest, a prince or an individual. However, with regard to all other sins which are punishable (if done with intent) by kareth (extirpation) if a regular person performs them s/he brings a she-goat or a female ship, but the prince brings a he-goat.
Tractate Horayot, which means teachings discusses various situations where a court has made a mistake, and in which of these situations the court must bring a bull to atone for its mistake but those who accidentally sinned are not liable to bring a sacrifice. The tractate also talks about those cases in which the court is not liable but the actual sinners are liable for a sacrifice.
The reason that this tractate is part of Seder Nezikin is that it is directed to judges, the subject of tractate Sanhedrin and Makkot. It is last in the order because it is the shortest of Nezikins tractates.