It follows the Hijri calendar (5)
I believe the answer is:
islam
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">it follows the hijri calendar</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for islam that I've seen before include "Major world religion" , "Religion based on Muhammad's teachings" , "Religion based on teachings of Muhammad" , "Religious faith of Muslims" , "Mails to great eastern religion" .)