means Specialized vocabulary used within a particular group, trade, or profession that often sounds like gibberish to everyone outside it.

from From Old French 'jargon,' meaning the twittering or warbling of birds — chatter so rapid and unintelligible it might as well be birdsong. The French word likely came from an imitative root mimicking that meaningless babble. So when your accountant talks 'amortized depreciation,' you're hearing, etymologically speaking, a flock of starlings.