OT3
From Super-wiki
OT3 is a variation on the term OTP - one true pairing - and refers to a threesome that a fan adores. Generally used playfully, if there is any OT3 in Supernatural it is Dean/Sam/Castiel aka Team Free Will.
Of course alternate OT3 pairings are also known in the fandom, like Dean/Castiel/Gabriel.
Links
- Two Angels and a Human Dean/Castiel/Gabriel community at LJ