What is the meaning of Tawhid? And what are its categories?

Linguistically, Tawhid means: Singling out Allah Almighty in His Oneness. Technically, it means: Singling Him out in what is specific to Him regarding His Divinity (uluhiyyah), Lordship (rububiyyah), Names, and Attributes. The sacred texts in the Qur’an and Sunnah have affirmed its status and importance, among them the Almighty’s saying: "Say, 'He is Allah, [who is] One,'" and the Prophet’s (peace be upon him) saying: "Islam is built upon five [pillars]: ...that Allah be worshipped alone [or: that Allah be declared One]."

Tawhid is divided into three categories: 1. Tawhid al-Rububiyyah (Oneness of Lordship): Singling out Allah Almighty in His actions, such as creation, dominion, and governance. The disbelievers of Quraish acknowledged this. 2. Tawhid al-Uluhiyyah (Oneness of Divinity): Singling out Allah Almighty in all apparent and hidden forms of worship. This is what the messengers were sent for and the books were revealed for. It is also called Tawhid al-Ibadah (Oneness of Worship) or Tawhid al-Qasd (Oneness of Intention). 3. Tawhid al-Asma wa al-Sifat (Oneness of Names and Attributes): Singling out Allah Almighty in His Names and Attributes that He affirmed for Himself or that His Prophet affirmed for Him, while purifying Him from all imperfections or resemblance to His creation.