I would like to know the meaning of the word 'Salaf' and who are the Salafiyoon (Salafis)?
The Salaf are Ahlus-Sunnah wal Jamaa'ah, those who follow Muhammad - صلى الله عليه وسلم – from the companions and those who follow their methodology/way until the Day of Resurrection.
When the Messenger - صلى الله عليه وسلم - was asked about the victorious group he said;
"Those who are upon what I and my companions are upon."
Fataawah al-Lajnah ad-Daa-imah: 2/164
What is Salafiyyah and what is your opinion of it?
Salafiyyah is an attribution to the righteous Salaf, and they are the companions of the Messenger of Allah - صلى الله عليه وسلم - and the Imaams of guidance from the first three generations – may Allah be pleased with them – those who were declared to be upon goodness by the Messenger of Allaah in his statement:
"The best of people are my generation, then those who come after them, then those who come after them. Then there will come a people whose witness would be preceded by an oath and whose oaths would be preceded by their witness." 
Collected by al-Imaan Ahmad in his Musnad as well as al-Bukhaari and Muslim.
'Salafiyoon' in the plural for the attribution 'Salafi', and its meaning has preceeded; those who are upon the methodology/way of the Salaf, who adhered to the Book and the Sunnah, called to it and acted upon it. Due to this, they are known as Ahlus-Sunnah wal Jamaa’ah.
And success lies with Allah and may the Salaat and the Salaam be upon our prophet Muhammad and his family and companions.
Fataawah al-Lajnah ad-Daa-imah: 1/165
The Permanent Committee for Scholarly Research and Religious Verdicts.
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1. An-Nawawee stated: This is a rebuke for those who bear witness and combine their witness with oaths.