Spanish, being such a vocabulary and synonym rich language, you'll find at least three or four different terms that adequately convey the broad meaning of almost concept that you wish to articulate, however most of the time, there are subtle nuances and implied meanings (connotations) when using different words for the same concept.. Add regionalisms to the mix, and using the "right" word becomes a fun task to say the least.
This is a good example: since Jerga certainly conveys the meaning of slang it is nonetheless a very neutral, "internationalized - standard" word that most people with at least a high-school level vocabulary will understand both in Spain, and Hispanic America. It does, however sound a little "off" in everyday speech.
A more accurate term in common use for 'slang' in México is Caló (There even used to be a rap band named exactly that! Caló: El Cubo even though the vocalist can rap, the rest of the act is embarrassingly kitsch.)
Coloquial is also a good, standard term for 'slang'. However,Jerga , Caló, and Coloquial are hardly ever used outside formal linguistic studies.
Most Mexican Spanish speakers will qualify speech as "corriente" (cheap) as in "su forma de hablar es muy corriente / it is a very cheap way of talking". Mexico City favors the more insular Guarro but that has a heavy rudeness connotation. Lately, "naco" has also been used to describe slang, though that has a connotation of ignorance and unsophistication, (usaste una frase muy naca / you used a very kitsch phrase).
Its probably worth mentioning that at least in Mexico, the very word "Slang" is well understood with the same meaning as in English as a kind of "loan word". That may not hold true in Central America or Spain, though.
In conclusion, be safe and use "Coloquial", or even "Slang". Or have some fun and try your luck with Naco, its probably not any worse than whatever actual slang you may be pointing out =)