What is the meaning of ?

The katakana syllable (ro). Its equivalent in hiragana is (ro). It is the forty-third syllable in the gojūon order; its position is (ra-gyō o-dan, row ra, section o).

short form for Russia or Russian, Russo- (prefix), short form of ロシア (Roshia), also written in kanji: (ろ, Ro).

si (musical note)

Source: wiktionary.org