Definition:Calendar/Muslim

Definition
The Muslim calendar is a calendar whose period is based on $12$ full cycles of phases of the moon.

Each Muslim year lasts either $354$ or $355$ days, depending on precisely when the relevant new moons happen

The years are numbered from the year when Muhammad and his followers migrated from Mecca to Medina in $622 \, \text{A.D}$ by the Julian calendar.

Years are denoted with the suffix $\text{A.H.}$, meaning Anno Hegirae, literally in the year of the Hejira.

The start and end of the Muslim year are $10$ to $12$ days earlier every civil year.

The $354$ or $355$ days in the Muslim year are divided into $12$ approximately equal sections called months, each either $29$ or $30$ days, depending on the phases of the moon.

They are assigned both names and index numbers:

Also known as
The Muslim calendar is also known as the Hijri calendar or the Islamic calendar.