(from the Heroes TV series)
Yatta is a Japanese short form for "yarimashita", which translates to "(I/We) did it!", but can also have meanings of "okay!", "it's done!", "ready!", or "all right!". The word is frequently exclaimed by Hiro Nakamura, accompanied by his raised arms.
http://www.urbandictionary.com/define.php?term=yatta
In Japanese, it means "I did it" or "I did something". A Japanese song called, "Yatta" was written, and it repeats the word "yatta". It can be a proclamation of success. "Yatta" can also be like "Eureka!" or another term of that nature.
To clarify the other definitions, yatta is a general japanese term used to express great happiness.
