Sayyid is an honorific title of Hasanid and Husaynid lineage, recognized as descendants of the Islamic prophet Muhammad through his daughter Fatima and Ali's sons Hasan and Husayn. The title may also refer to the descendants of the family of the Bani Hashim through the Prophet's great-grandfather Hashim, and others including Hamza, Abbas, Abu Talib, and Asad ibn Hashim.

See also Sharif, which has a good description of three types of identification for that term and co-relates to this term. In its narrowest sense, a sayyid is a descendant of Husayn ibn Ali, but the term is also more generally used for descendants of The Prophet.

A few Arabic language experts state that "Sayyid" has its roots in the word al-asad الأسد, meaning "lion", probably because of the qualities of valor and leadership. The word is derived from the verb sāda, meaning to rule. The title seyyed/sayyid/syed/sayyad/saeed/said existed before Islam, however not in light of a specific descent, but as a meritocratic sign of respect.

Hans Wehr's Dictionary of Modern Written Arabic defines seyyid as a translation for master, chief, sovereign, or lord. It also denotes someone respected and of high status.

In the Arab world, sayyid is the equivalent of the English word "liege lord" or "master".

The foundation of the title Sayyid is unclear. In fact the title Sayyid as a unified reference for descendants of Muhammad did not exist, according to Morimoto Kazuo, until the Mongol conquests. This can be substantiated by historic records about Abdul Qadir Gilani and Baha' al-Din Naqshband, who did not refer to themselves with any title, despite their lineages to Muhammad. Sometimes the ruling community of a nation took this title to portray themselves as respected and honored, though they are not actually the descendants of Muhammad. This gives reasons to think that this title is founded later on.^{[citation needed]} Morimoto refers to Mominov, who describes that the emergence of a community leader during the Mongol era (Ilkhanate) gave rise to the prominence of the title Sayyid. This leader is most probably the Sunni Shafi'ite scholar Mir Sayyid Ali Hamadani, who lived in this time, being known as a saint credited with the honorific titles "Amir-e-Kabir" (English: "Grand Prince") and "Ali-e-Sani" (English: "Second Ali"). Hamadani's religious legacy in Kashmir as well as his headquarter (Persian: Khanqah) the Khanqa-e-Mola became under the control of the Grand Sayyid Hazrat Ishaan. Hazrat Ishaan's descendants are buried in Hamadani's headquarters, on which occasion it is known as the Ziyarat Naqshband Sahab today.

However, in Sunni Islam as practiced in the Ottoman and Mughal Empire, a person descending from Muhammad (either maternally or paternally) can only claim the title of Sayyid meritocratically by passing audits, whereupon exclusive rights, like paying lesser taxes, will be granted. These are mostly based on the claimant's demonstrated knowledge of the Quran and piousness (Arabic: Taqwa) under the assessment of a Naqib al-Ashraf, also known as a Mir in Persian-speaking countries. Notable examples of such a Naqib (plural: "Nuqaba") or Mirs (plural: "Miran"), were Hazrat Ishaan in the Mughal Empire and his descendant Sayyid Mir Fazlullah Agha in Royal Afghanistan.

Men belonging to the Sayyid families or tribes in the Arab world used to wear white- or ivory-coloured daggers like jambiyas, khanjars or shibriyas to demarcate their nobility amongst other Arab men, although this custom has been restricted due to the local laws of the variously divided Arab countries.^{[citation needed]}