Keiko and Renshuu are two terms that usually come out in English as “practice”. However, they are not interchangeable. In fact, they should be constantly combined.
As one instructor explained, etymologically, renshuu looks like this:
練習 (れんしゅう) – the kanji for “practice, drill, polish, refine” plus the kanji for “learn.” The suggested meaning therefore is to learn something through repetition, with the implication that a lot of repetition would also lead to refinement of technique.
Another way of expressing it would simply be “drill”.
Whereas keiko:
稽古 (けいこ) – combines the kanji for “think or consider” with the kanji for “old.” It has the sense of reflecting on the past, showing respect for those who have gone before, and trying to understand their legacy.
Together the two terms encompass what should be our goal, i.e., to appreciate our inheritance and to strive to improve through attentive effort.