A Marriage cake is a ceremonial cake of the Argosians on the planet Argos. When a cake is presented, it signifies the bearer's wish to marry. Receiving and eating the cake indicates acceptance of the proposal.
The contents of the cake were sufficient to drug Colonel Jack O'Neill, who in a romantic interlude with an Argosian woman, Kynthia, and was inadvertently infected with microscopic nanites created by the Goa'uld Pelops. (SG1: "Brief Candle")