What's the meaning of the Japanese name Ryoku?

Answer 1

力 - (ryoku) - means "power" or "strength" in Japanese

I don't think this is a common name, though...

Answer 2

It is an uncommon name, and there is no way to know its meaning for certain without knowing which kanji is used.
(In most cased, the meaning of a name is determined by kanji rather than in pronounciation.)

One possibility is 力, as Rabbityama has pointed out, meaning strength or power, but then it's usually prounced 'riki' or 'chikara' when it's used as a name.
Another is 緑 meaning green, which is usually pronounced 'midori'.