The standard language of a particular country or locality. It would be the language of the person in the street—not necessarily what is taught in the schools for that locale. If your writing includes characters who are likely to be speaking in the local vernacular, you will want to include enough of it to flavor the story, but too much slows down the action and is hard to read. When using it, never assume you can duplicate the vernacular accurately when you are not familiar with it. It’s always best to have someone familiar with the vernacular read your material to be sure you have portrayed it accurately. The advent of cell phones and texting is creating a new vernacular for today's teens and young adults. Vernacular would also include slang, or even the way people in a particular profession speak to each other. For much more on vernacular, go to: http://xroads.virginia.edu/~hyper/made/ch02.html.