Creature that seeks out a host, empowering it to live either parasitically (the Goa'uld) or symbiotically (the Tok'ra). Utterly helpless outside of its natural water environment, a symbiote requires either a minute electrical current in a liquid habitat, or a living host to survive.
The immature, larval form of a symbiote is called a prim'tah.
Children of the Gods - Teal'c displays his symbiote to his teammates to show them what it is.
The Enemy Within - Teal'c confirms he is still carrying his symbiote after Major Kawalsky is possessed by one.
The First Ones - SG-1 visits the original homeworld of the Goa'uld, where a primitive symbiote leaps from a lake and nearly reaches Daniel.
Last Stand - Daniel is surprised to see the System Lords partake in a "feast" at their summit, consuming live symbiotes of their own kind.
Abyss - The Tok'ra symbiote Kanan leaves Jack O'Neill's body and dies in an attempt to escape from Baal.