Hullin means non-sanctified things. As the name of our tractate it refers to non-sacrificial meat, the topic that most of our tractate deals with. It is indeed the opposite of what Seder Kodashim is all about—holy meat. The meat in our tractate is thus called by what it is not.
We should note that according to many biblical scholars, before the Temple was established, all meat that was eaten would have been sacrificial. A person who wanted to eat meat would bring an animal to the local sanctuary where it would be slaughtered. Some of the meat would be given to the priests, and the remainder could be eaten by the owners. When the Temple was established, it became prohibited to offer sacrifices anywhere but the Temple in Jerusalem and therefore people who wanted to eat meat had to eat it in a non-sacrificial manner.
Deuteronomy 12:20-24 teaches what one is to do should one want to eat non-sacrificial meat.
20 When the LORD enlarges your territory, as He has promised you, and you say, "I shall eat some meat," for you have the urge to eat meat, you may eat meat whenever you wish. 21 If the place where the LORD has chosen to establish His name is too far from you, you may slaughter any of the cattle or sheep that the LORD gives you, as I have instructed you; and you may eat to your heart's content in your settlements. 22 Eat it, however, as the gazelle and the deer are eaten: the unclean may eat it together with the clean. 23 But make sure that you do not partake of the blood; for the blood is the life, and you must not consume the life with the flesh. 24 You must not partake of it; you must pour it out on the ground like water: 25 you must not partake of it, in order that it may go well with you and with your descendants to come, for you will be doing what is right in the sight of the LORD. 26 But such sacred and votive donations as you may have shall be taken by you to the site that the LORD will choose.
The Torah itself does not describe how meat is supposed to be slaughtered. However, by the very need to drain the blood (vs. 23) it is likely that the Torah presumes that the animal’s neck will be sliced. The other laws of “shechitah”—slaughtering, are oral laws, transmitted by Jewish tradition, but not found in the Torah. Our tractate will deal with these laws at length.
In order to make the tractate a bit easier I will explain two terms here that will come up throughout: Nevelah: An animal that died without having been properly slaughtered. See Deuteronomy 14:21. Terefah: An animal that is wounded or sick and will eminently die. Such an animal is prohibited even if it is properly slaughtered. The word “treif” which colloquially is used to mean “unkosher” comes from this word.
There are other prohibitions concerning slaughtering and eating animals that come up throughout the tractate, but I shall introduce them as we go along.
As we learn the tractate we should remember that despite the fact that most of us do not slaughter our own meat, and hence these laws are not really practical for us, they are still observed today, and indeed until recently, before refrigeration was invented, all slaughtering would have been local. “Buy local” wasn’t just an environmental slogan; it was a culinary necessity. Hence, butchers would have been found in every community. Indeed, when Jews moved to a new place first and foremost they needed three things: a mikveh for women to immerse in, a mohel and a shochet. Without these three institutions, no traditional Jewish community could exist. Furthermore, we should remember that usually a person would raise his own animals and then bring them to the shochet for him to slaughter. People would have seen the slaughtering occur, and while not everyone was an expert in these laws and many people never performed them, they would have at least seen them being performed. Personally, I think that the study of Tractate Hullin is a good opportunity for us to reflect on the meaning of eating meat in our society and in our personal lives.
Enjoy the Tractate!