More than 10,000 companions of the Prophet are buried here. So this cemetery represents a piece of heaven to Medina's people and many Muslims. It's located just right beside the Prophet's Mosque.
It is said that the youngest daughter of the Prophet 'Fatima az Zahra' is buried here too, but there're other sayings as well.
Muslims after they visit the Prophet's mosque and tomb, they visit this cemetery to greet the companions and the other dead. It is costumary for Muslims to send greetings of peace to the dead.
Women are not allowed in and sometime men are not allowed in either. It gets very crowded.
Many Muslims wish to be buried in this cemetery. Since it gets too full, if the person doesn't live in Medina but coming from a different city, they need a permission to bury the dead in here. Other time, it's just allowed depending how busy it gets.
This cemetery is only for Sunni Muslims; Wahhabis, Sufis or whatever. There is another cemetery for Shaiit Muslims.
The tomb's top level should not exceed 30 cm, no stones or domes should be built on the grave(Wahhabi belief).
So all Muslim dress code regulations and Muslim customs apply. They are even more strict in Madinah and Mecca though due to the presence of religious police, who sometimes even harass people who are breaking no rule, but who are not following the strict Wahhabi interpertation of Islam.
Some things must always be done, like a woman must always cover her head, and should not venture outside without a male relative. Males too must follow a dresscode, and shouldn't wear shorts, or anything that would expose their arms.