The term "extra-cock" is a creative and alternative phrase used to describe the act of having two cocks in a scene, typically referring to a threesome involving three men. This tag can be found in porn videos that feature this type of sexual encounter. The word "extra" highlights the idea of an additional participant with a penis in the scene, while "cock" remains a popular and straightforward term for the male genitalia. Overall, this tag is meant to convey the presence of three men engaging in intimate activities together, where two of them have penises.