What does "idiomatic Ruby" mean?

From a chat with Mark today, in regard to reading a post where I used the word "idiomatic":

(10:10:42) Mark: idiomatic, what a word
(10:11:12) Scott Porad: yes, i don't even know what it means...but people 
say it when they mean, "there's a more clever way to write this in ruby".
(10:11:26) Mark: Peculiar to or characteristic of a given language.
(10:12:05) Mark: nice, one of the descriptions of idiomatic, uses idiomatic 
to describe it: Characterized by proficient use of idiomatic expressions