Short for the Mexican slang word "Orale". It is usually defined by what follows the word since it has multiple meanings.
The shortening of the word is most commonly used in Twitter where character counts are limited to only 140 per tweet. In this case, 'Ora' is usually followed by a persons username to bring a tweet to their attention as in saying "Yo, you hear that?" Or "Look, they're talking about you".
Ora @ladygaga RT @Facts: The word "Gaga" in Filipino refers to a stupid and idiotic girl.