jargon: a barbarous, rude, or debased variety of speech; lingo
Despite the Oxford English Dictionary's insistence that jargon is barbarous, a lot of writing uses it - particularly novels for teens. In fact, a number of acclaimed novels for teens have used it: M.T. Anderson's FEED and Paolo Bacigalupi's SHIP BREAKER are just two examples. You might have used jargon in your novel. Quite often, the jargon is invented, as a part of the new world that the novel is set in.
HOWEVER, this is something you want to keep out of your query letter. Jargon is specific to a generation, a geographical area, sometimes even a gender. The jargon in your book is probably specific to your book. Taken out of the context of your novel, it could be confusing and need too much explaining, and you don't have time for wasted words in a query letter.
So, even though you want the voice in your query letter to match the voice in your manuscript, try to do it without using jargon.
Do you use jargon in your novel?