Japanese for "useless" or "futile" they both mean the same.
Repeating the word while overhwelming an hopeless enemy with rapid attacks became a fad on the internet with a flash animation that is based on the PlayStation game Jojo's Bizzare Adventure
that is also an Japanese anime
Sometimes spelled "mudah."
Also see ora
During his famous "Road Roller Da" attack Dio Brando drops a hugeass steamroller on his opponent, screams the famous "WRYYY" shout (though originally he just laughs) and punches the steamroller, crushing it more on the enemy shouting "MUDA MUDA MUDA MUDA!" repeatedly, resulting in total ownage.