I read it as being able to pass coded messages while engaging in what appears to be mundane conversation or possibly using a secret language to communicate with others of your "brethren" (like DnD's Thieves Cant).
Jargon is the ability to use "professional slang" that is specific to a certain industry to pretend to be competent at it.
For instance, if you were posing as a Doctor, you could use Deception/Jargon to tell someone they have accute hemotosis of the neural catheter. A person who isn't a doctor might easily be fooled by that, thinking they have a serious medical condition, when in fact, it is just word salad.
This can work with a lot of highly technical jobs that have their own vocabulary. You can pass yourself off as everything from a Catholic priest to a scientist or a mechanic using Jargon.
Secret Codes would be cryptography, which might be a specialization in a different skill.