The word "Tahabit" is an acronymn created from the four Hebrew words "Torah" (the Five Books of Mosha), "Haftara" (the weekly reading accompanied with Torah), "Bes[h]ura" (Good News), and "Igeret" (Epistle/Letter). A part of the acronymn includes the last letter of the word "Igeret" (t).
Sefer Tahabit is a collection of the weekly readings from the above sources used in communities of the Nesarim. Sefer Tahabit is in Hebrew and is now gradually being made available in English.