The institutional nature of the Halakhah found its expression int he terms which are used to refer to it in the earliest sources at our disposal. The halakhot from the period of the Pairs (Zugot) and the early tanna’im are referred to as gezerot and takkanot. The only difference between them is that the latter were regulations intended to correct a situation in a positive manner whereas the gezerah is prohibitive and restrictive. The gezerah is identical to the seyag (fence) in the aphorism attributed to the Men of the Great Assembly, “Make a seyag around the Torah.” There is nothing new in a gezerah, it just places a protective fence, so to speak, around a Torah commandment in order to “keep people from transgressing it” (Berakhot 1:1).
The takkanah, on the other hand, initiates something new and thus it corrects an aberration which has developed.
Ephraim E. Urbach, The Halakhah: Its Sources and Development, trans. Raphael Posner (Ramat Gan: Massada; Jerusalem: Yad la-Talmud, 1986), 7.