look up any word, like cunt:
 
1.
Young women, usually overweight, that are so egocetnric and self-absorbed that they make up cute little words to describe themselves and their so-called "friendship".
Those three fatties we met from Wisconsin seemed cool at first, but then they turned out to be total thrins.
by Joe Borczack March 31, 2007
 
2.
A group of three friends who are very close, like sisters. Like twins, only three.
Maddy, Rikki, and Miranda were better known as "The Thrins" at school.
by Spazzy McGee October 29, 2006