Sam/Eileen fanworks pairs the characters Sam Winchester and Eileen Leahy in a romantic or sexual relationship. The pairing is sometimes referred to by the portmanteau Saileen.
Fans spotted a connection between Sam and Eileen when they first meet while on a banshee hunt in 11.11 Into the Mystic.
In 15.07 Last Call, following her resurrection Sam and Eileen spend more time including a night of many margaritas. During a session of research (not a euphemism) they make moves towards a kiss when they are interrupted by Castiel's return.