Venom is any of a variety of toxins used by certain types of animals. Generally, venom is injected by such means as a bite or a sting.
The Infestation fly administers a venom into Humans used for reproduction. It contains a retrovirus that causes the human's DNA to be modified to the bug's DNA, then wraps them in a cocoon, and kills them with roughly 10 bugs coming out of them. Dr. Timothy Harlow created an antivenom that could slow the metamorphosis caused by the venom and, with help, reverse its effects. (SG1: "Bane")
Squigglers injected a venom into people, if they didn't kill them, which in small doses, was able to kill off the Hoth virus. Lt. Tamara Johansen later used this venom as a type of Anesthetic to sedate Dr. Nicholas Rush. (SGU: "Time", "Divided")