SAIYID. صيد
A term used for the descendants of Muhammad from his daughter Fatimah by ‘Ali. The word only occurs twice in the Qur’an – in Surah iii. 34, where it is used for John Baptist; and in Surah xii. 25, where it stands for the husband of Zalikhah. According to the Majmu ‘l-Bihar, p. 151, it means “lord, king, exalted, saint, merciful, meek, husband,” &c.
There are two branches of Saiyids – those descended from al-Hasan and those descended from al-Hussin (both the sons of ‘Ali.)
These descendants of Muhammad are prayed for at every period of the daily prayers [PRAYERS], and they are held in all Muslim countries in the highest respect, however poor or degraded their position may be.
The term Saiyid is also given as a name to persons who are not descended from Muhammad, e.g. Saiyid Shah, Saiyid Amin, &e., although it is a mere assumption, in addition to the term Saiyid, the term Badshah, Shah, Mir, and Sharif, are applied to those descended from Bibi Fatimah.
The author of the Akhlaq-i-Jalali estimated in his day the descendants of Muhammad to be not less than 200,000.

Based on Hughes, Dictionary of Islam