An areola 51 exists when a woman's areola are mysteriously large and might be big enough to house aliens.
"Wow, i bet that girl last night was awesome, she was holding a monster rack"
"Yeah, they looked perky but once the bra came off, I saw areola 51 and ran because I dont want to deal with no aliens living on her frisbee nipples"
The skin around a woman's or men's nipple that is a different color than the person's skin tone. Areola51 specifically refers to the abnormally large or otherwise irregular and disgusting areolas.
I was about to run train on that skank
from last night but before getting into the deed I noticed she had some areola51 going on and couldn't help but barf