What is the meaning of ろ?
The hiragana syllable ろ (ro). Its equivalent in katakana is ロ (ro). It is the forty-third syllable in the gojūon order; its position is ら行お段 (ra-gyō o-dan, “row ra, section o”).
炉: furnace, kiln
denotes endearment
Source: wiktionary.org