Tawheed means Oneness and Uniqueness of Allah.
Islam is an Arabic word, which comes from the word ‘Salm’ which means peace and from 'Silm', which means submitting your will to Allah. Islam believes in 'Tawheed' which is not merely monotheism i.e. belief in one unique God, but much more. Tawheed literally means "unification" i.e. "asserting oneness" and is derived from the Arabic verb 'Wahhada' which means to unite, unify or consolidate. Tawheed can be divided into three categories.
(i) Tawheed ar-Ruboobeeyah (maintaining the unity of Lordship).
(ii) Tawheed al-Asmaa-was-sifaat (maintaining the unity of Allah's name and attributes).
(iii) Tawheed al-Ibaadah (maintaining the unity of worship).
The Qur’an reminds us of the falsity of all alleged gods. To the worshippers of man-made objects it asks: “Worship ye that which ye have (yourselves) carved? But Allah has created you and your handwork.” (Quran 37:95-96)
“Say: ‘Do ye then take (for worship) protectors other than Him, such as have no power either for good or for harm to themselves?” (Quran 13:16)
The Prophet Muhammad (PBUH) was asked by his contemporaries about Allah. The answer came directly from God Himself in the form of a short chapter of the Quran that is considered the essence of the Unity of God or the motto of monotheism. “Say: He is Allah, the One; Allah, the Eternal, Absolute; He begetteth not, nor is He begotten, and there is none like unto Him.” (Quran 112:1-4) The Quran repeats the attributes of Allah very frequently. “Allah! There is no god but He, the Living, the Self-subsisting, Eternal. No slumber can seize Him nor sleep. His are all things in the heavens and on earth. Who is there can intercede in His presence except as He permitteth? He knoweth what (appeareth to His creatures as) before or after or behind them. Nor shall they compass aught of His knowledge except as He willeth. His Throne doth extend over the heavens and the earth, and He feeleth no fatigue in guarding and preserving them for He is the Most High, the Supreme (in glory).” (Quran 2:255)