Sentence:  All these terms referencing the work of the Holy Spirit—coming upon, falling upon, being filled with the Holy Spirit, receiving the promise of the Father—can best be understood as synonymous with baptism in the Holy Spirit, with the key to understanding being “one baptism, many <WSD>fillings</WSD>.” 
Meaning of the word marked with <WSD> tags:  A religious experience attributed to the Holy Ghost "filling" a believer. (since late 19th or early 20th c.)