intercession

Tawassul is an Arabic word originated from wasilat.

It is not a disturbing innovation to visit the graveyards generally and seek forgiveness during the visit of the Prophet (P) and Infallible Imams' graves. There are some verses and traditionsthat legitimize the practice.   

The difference between Polytheism and Intercession is that there is a "transverse relationship" toward Allah in the polytheism, while in the intercession the relationship is longitudinal!

The prophet has also said,
I have received five gifts from God, one of which is that of intercession, which I have in store for my community, my intercession is for those who have not associated any partner with God...

One of the beliefs of the Shiites is intercession. The Wahhabis maintain that having such belief drives man to inclination toward committing sins while not only intercession does not make man careless of commiting sins but it prevents him from it.

Intercession is a belief of the Shiites which is confirmed by the verses of the Quran and the ahadith of the infallibles.

Only Allah deserves to be worshipped and asked for help. The belief of intercession is in line with this kind of oneness.