Wincest

Wincest is the term used to refer to slash pairing between the Winchesters, most commonly Sam and Dean, involving sexual situations.

The Wincest Fandom
Although the first Wincest fan fiction appeared online shortly after the airing of the Pilot, it was not until a few weeks later that the term "Wincest" was coined to refer to the slash pairing of Winchesters, a portmanteau of the name Winchester and Incest.

At first, Wincest involved all three known Winchester men: John, Sam and Dean. Later however, fan fictions and work pairing John with his sons was termed "Daddycest". Thus, Wincest began to mean sexual situations between solely Sam and Dean.

With the introduction of Adam Milligan, the Winchesters' younger half-brother, fans began pairing Adam with his two other brothers and father as he is technically a Winchester, thus, making the term "Wincest" applicable to him as well.