An attempt to communicate with the dead. The seance, or sitting, is led by a medium who goes into a trance that theoretically allows the dead to communicate through him or her.
The seance incantation used by Sam in 2.13 Houses of the Holy is "Amate spiritus obscure te quaerimus. Te oramus, nobiscum colloquere apud nos circita." The entire ceremony is as follows, taken from John Winchester's Journal by Alex Irvine: September 28: Séance: "On a clean altar cloth place a small bowl filled with fresh herbs. Around the perimeter of the cloth, place black and white candles alternating and equal in number. When all of the candles are lit, recite the following: Amate spiritus obscure te quaerimus. Te oramus, nobiscum colloquere apud nos circita. At the finish of the incantation, pinch a tiny amount of frankincense, sandalwood, or cinnamon powder over one of the candle flames."
In 4.01 Lazarus Rising, Pamela Barnes conducts a seance in the hopes of glimpsing what creature pulled Dean out of Hell. Sam, Dean, Bobby, and Pamela sit around a table. A black cloth with symbols on it covers the table, and six lit candles are placed in the center. The four join hands, and Pamela touches the hand print on Dean's shoulder that was left by the being. Pamela recites the phrase "I invoke, conjure, and command you, appear unto me before this circle" multiple times. She hears the being say that it is Castiel, and that she should stop the ritual. She refuses, and begins repeating "I conjure and command you, show me your face." When she catches a psychic glimpse of Castiel, her eyes are burned out.