Shaykh Saalih Aal al-Shaykh, stated:

Muslims are of two groups: Salafis and Khalafis. As for the Salafis, then they are the followers of al-Salaf al-Saalih (first three generations of Muslims). And as for the Khalafis, then they are the followers of the understanding of the Khalaf [the later ones or strayers from the Salafi way] and they are also called Innovators - since everyone who is not pleased and satisfied with the path of the Salaf us-Saalih, in knowledge and action, understanding and fiqh, then he is a khalafi, an innovator...

Source: In his book "Haadhihi Mafaaheemunaa", a refutation of Muhammad Alawi al-Maliki, [Chapter on Ascription Salaf and Salafiyyah]

Notes:

The quote above comprises and indication why many Muslim factions, groups and parties feel threatened by and resent ascription to "Salafiyyah." It is because Salafiyyah is not an ascription to one man, one party or one sect. Rather, it is an ascription to that which cannot collectively err, which is the entire body of the Companions, and whoever took from them and then whoever took from them. Unlike, the parties, groups and sects, whose doctrines and methodologies are based primarily upon a single man and his works, the Salafi understanding of the Book and the Sunnah is based upon those praised in the revealed texts and those made worthy of being followed through revealed texts, and who collectively do not err. Because only the Salafis can truthfully claim that they are following this way, the various parties and factions (like the Ash'aris, Maturidis, Ikhwanis, Sufis, Tablighis, Tahriris, Takfiris) and other than them feel threatened by Salafiyyah because they all know full well that their doctrines and methodologes do not trace back to the Salaf, fundamentally, but to the Khalaf, or to individual men and their books. This matter will be elaborated upon in more detail in other articles.