From the Greek word meaning "glory," a kudos is acclaim for exceptional achievement or qualities.
On the RP repository, receiving a kudos means that another community member recommends you as someone other people might like to get to know. Perhaps because you are exceptionally fun to RP with, exceptionally fun to know, or are just plain exceptional!
Yes, I realize that my last kudos for Minkja also mentioned Roll and Initative, but that's how awesome they are.