An obsolete form of lower-case s, written or printed as ſ. It was used in initial and medial but not final position in a word, and was generally abandoned in English-language printing shortly before 1800.
小写s，印刷体f.（置于词首或词中，1800年前不久废除）
Definition of long s in US English:
long s
noun
An obsolete form of lower-case s, written or printed as ſ. It was used in initial and medial but not final position in a word, and was generally abandoned in English-language printing shortly before 1800.