Salik is a term for a follower of Sufism. Its root is the verb salaka which means to travel or follow. It is related to suluk "pathway". Suluk here specifically refers to a spiritual path, i.e. the combination of the two "paths" that can be followed in religion, the exoteric path or shariah, and the esoteric path or haqiqa. The "path" metaphor is derived from the Qur'an: see sura 16, (An-Nahl, The Bees), ayat 69:

fasluki subula rabbiki dhululan "and follow the ways of your Lord made easy [for you]", which uses the imperative of the verb salaka which means to follow or to travel