A harcesis is a child born from two Goa'uld hosts. This is considered forbidden by the Goa'uld System Lords because the Goa'uld genetic memory is passed down to the offspring, making the child a threat. (Goa'uld reproduce their own kind asexually spawned from a queen.) The harcesis possesses all the knowledge of the Goa'uld who fathered it. A harcesis threatens the Goa'uld power structure by simply being able to tell people that they were not gods and the truth behind their technology or how to use it. In 1938, Aset gave birth to a harcesis child, but Serqet informed Ra and he dealt with that transgression swiftly (Stargate Origins). SG-1 once sought the child of Apophis and Amaunet, but the infant, Shifu, was found to be under the protection of the powerful being Oma Desala. (SG1: "Maternal Instinct", "Absolute Power")
While not a true Harcesis, an experiment by NID operative Doctor Keffler resulted in the creation of Anna, a human/Goa'uld hybrid created by combining a human ovum with DNA from the symbiote of the Goa'uld Sekhmet, granting Anna access to the knowledge of Sekhmet, although this only occurred when she slept and also resulted in Sekhmet's personality taking control of her (SG1: "Resurrection").