In a general sense, when referring to Islam within its own fold define sects in relation to belief in God, that is, if the person believes in the proper definition of God or not: this is what is called Aqeeda.
Aqeeda is in reference to the proper metaphysics of God in the sense that believing in God but not believing God is Eternal or Omnipotent puts you out of the fold of orthodox Islam.
It has less to do with labels, more with beliefs. From that sense, a Shi'a is also a part of the Ahlus Sunnah whereas a Wahhabi isn't. This is because Shiites believe in God being Omnipotent, Eternal, and most important of all, Transcendent, whereas the Wahhabi believes that God is a physical man in the clouds above.
Most sectarian debates include whether one can pray behind a person of a certain sect and this is where belief in God is important because you are praying to God, not 'Umar ibn al-Khattab or 'Ali, so you might love 'Umar all you want and not curse him as the Shiites are accused of doing quite often but if you are praying to a God who is a man in the clouds with limits – and yes the Wahhabi Muslims believe God has limits, we just do not know of them but He does – then sorry, I cannot pray behind you.
That is what defines a sect in Islam: belief in God, not keeping a fistful of beard or wearing a headscarf. If your understanding of God is weak or compromised, you are out of the greater fold of Islam, so you can reject the nuances all you want, it matters little as long as you believe about God what is correct to be believed within the fold of Islam that He is Eternal, Absolute, One, Omnipotent, Omniscient, Almighty, Transcendent, and Perfect, and that Muhammad is the last and final Messenger of God. Amen.
— Fahim Ferdous Promi