What is the meaning of る?

The hiragana syllable る (ru). Its equivalent in katakana is ル (ru). It is the forty-first syllable in the gojūon order; its position is ら行う段 (ra-gyō u-dan, “row ra, section u”).

A general method to form verbs (as a godan katsuyō verb). Much less productive than 〜する (-suru, “to do”).

the present progressive: to be doing