“Qira’at” refers to various methods of Quran Reading & Recitation. There are ten different well-known schools of qira’at, and each one deriving its name from a noted Quran reciter or “reader” (Qari).
Each Qirat is recited by the master with all variants. It is a kind of corpus of recitation, that is then referred to as the master by the students. There are many transmission lines as well. So in short, there there are 20 Rawis and Eighteen lines in total. Each Qirat has its own rules of recitaiotn and tajweed.