Belief in the Oneness of Allah [Monotheism]
To explain the notion of the oneness of Allah [Tawheed] we can split it into three parts:
(1) Tawhid al `Uluhiyyah (Oneness of the Worship of Allah)
(2) Tawhid al Rubu`biyah (Oneness of the Lordship of Allah) and
(3) Tawheed-al-Asma was-Sifaat (Oneness of the Names and the Attributes of Allah).