Sacrifices were not to be slaughtered outside the azarah, which is the courtyard of the Temple. Doing so, we are told incurs a penalty of kareis (spiritual excision).
The Talmud in Zevachim (106a) asks a very good question. We have a well-known principle that God doesn’t punish for an action unless He has also warned us about the deed in question. Our verse here states the penalty, but where’s the warning against the action itself? After some discussion, the Sages conclude that it is Deuteronomy 12:13, “Guard yourselves against offering your burnt offerings just any place you feel like.”
The reason underlying this mitzvah is that God designated a particular place for sacrifices so that people would be in awe of that place and turn their hearts to Him when they brought their sacrifices there. If sacrifices could be slaughtered any place one desired, neither the act of slaughtering nor the Temple itself would be as special in people’s eyes. Look at nowadays, the way in which many people justify, “I can just daven at home.” Just imagine how it would be if people could say, “Sure, I could bring this sacrifice all the way to the Temple, but it’s so much easier to just slaughter it in my back yard…”
In Mitzvah #439, in parshas Re’eh, we will see that there is an independent prohibition against offering up sacrifices outside the Temple. If a person both slaughtered an animal for a sacrifice outside the Temple and offered it up outside the Temple, he would violate two discrete mitzvos.
Surprisingly, this mitzvah is in effect today, even in the absence of the Temple. If a person were to slaughter an animal with the intention that it should serve as a sacrifice, he would be in violation of this mitzvah.
This mitzvah is the discussed in the Talmudic tractate of Zevachim on pages 106a-107a and in tractate Kerisos on page 3b. This mitzvah is codified in the Mishneh Torah in the eighteenth chapter of Hilchos Maaseh Hakarbanos and is #90 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos. It is not included in the Sefer HaMitzvos HaKatzar of the Chofetz Chaim.