It's a phrase used to address the two grandsons of the Prophet Muhammad, Imam Hasan and Imam Husayn. It's a common invocation in Shia Islam, often used in prayers, mourning rituals, and devotional practices.
Let's break it down:
* Ya: This is the Arabic word for "O" or "Oh," used to address someone directly.
* Hasan: This is the name of the elder grandson of the Prophet, known for his piety and peacefulness.
* Husayn: This is the name of the younger grandson of the Prophet, known for his courage and sacrifice.
So, "Ya Hasan Husayn" is a direct address and an expression of reverence towards these two important figures in Islamic history and faith.