As for Salafiyyah, its affair is clear. From the angle of the Arabic language it is an ascription to he who has proceeded, meaning he who has passed. So it is said about the one who has passed: He is Saalif (he has preceded). If man has precedence in anything, it is said that he has preceded it. And in the hadeeth:
"You have accepted Islaam with all the previous (aslafta) good you had practised"  - meaning that which has proceeded from before.