From The Stargate Omnipedia
The incubating chamber of Jaffa anatomy where a symbiote is stored. In exchange for survival within the pouch, the Goa'uld naturally gives its Jaffa freedom from most illnesses and a considerably increased lifespan of approximately 140 to 150 years.
Children of the Gods - Teal'c shows his symbiote pouch, as well as the Goa'uld within, to his future teammates, explaining its purpose.
Hathor - The Goa'uld queen Hathor uses her technology to create a symbiote pouch in Jack O'Neill's abdomen, which is healed when he is placed in a sarcophagus.
Crossroads - Teal'c learns in a vision that his father was murdered when Cronus reached into his symbiote pouch and crushed the larval Goa'uld within.