slang abbreviation for "natural". Usually used to refer to Natural Light beer. Also used in the health & fitness community to refer to bodybuilders who do not utilize performance-enhancing drugs, such as anabolic steroids.
1) Yo, someone toss me a natty from the fridge.
2) I don't care how big you can get on roids
...I'd rather be natty and 190 lbs., than 250 lbs. and juicing