Jargon is like an inside joke. It’s a word or phrase that means something to someone, but if you don’t know the backstory, it won’t mean much to you.
Lawyers, doctors, scientists, and other people whose jobs require a shitload of formal education use jargon so they won’t have to spend all day describing a complicated idea to someone who already understands it. If you’ve ever been to a hospital or seen one on television, you can appreciate why doctors need jargon. It’s a lot faster to say “I need eight million corpuscles of Vaxadrine and a canis major, stat”* than it is to say whatever you might have to say to a layperson to get the things you need.
Sadly, not everyone who uses jargon does so with your best interests in mind. In fact, some people use it because they don’t want you to understand what they’re saying.
Maybe they’re up to something really horrible, like killing innocent people in a war, so they tell you they did everything they could to reduce collateral damage. Or maybe they’re trying desperately to keep you from finding out that they never do anything interesting or important or complicated, so they say they’ve been busy applying pressure to tree-based ink-display solutions. People who talk to you like this do not respect you.
*Obviously I don’t speak doctor, but you get the idea.