Green’s Dictionary of Slang

encore n.

1. (US) a second helping.

[US]H.G. van Campen ‘Our Theatrical Boarding House’ in L.A. Herald 10 Dec. 10/4: ‘Encore the cake’.

2. sexual intercourse for the second time, usu. soon after one has just completed an initial bout.

[US]LektroMan ‘Watching Jerry Jerk’ on Nifty Erotic Stories Archive [Internet] We both must have silently feared that Brian would awake and discover our delicious secret. Perhaps he might even join in for an encore.
[US]J. Fonda ‘Richard’ on Nifty Erotic Stories Archive [Internet] He said, ‘Wow! That was great’, but we never got the chance for an encore.

In compounds

encore queen (n.)

(US gay) one who returns to former lovers.

[US]B. Rodgers Queens’ Vernacular 75: encore queen (fr Fr encore = yet, still, just once more) one who revisits ex-lovers.