This word is short version of "get together." It usually means just a small gathering of friends at a house. A lot of the times, there's alcohol involved. But it can totally become a party if people end up inviting people.
Examples of How to Use the Word:
"Oye, I heard that the getty is going to be at Giovanna's house tonight!"
"Are the dudes going to get some liquor? I am tired of getting alcohol for these damn gettys!"
"Bro, screw Danny's getty. I heard Carolina has a getty and she has unlimited Bacardi on deck. And you know that girl and her friends are HOTTTTT!"