Here's the simple version. Barclays did something so naughty, they were fined £300 million.
Here's the more complicated version. One part of Barclays is responsible for reporting the rates that they loan money overnight; that's combined with a dozen or so other banks reports to give LIBOR, the "London Interbank Overnight Rate".
Another part of Barclays does financial trades. If you know in advance what the LIBOR would be, well, it's a bit like knowing in advance which horse will win a race. If you bend your report of rates a bit, that's like influencing the result of the race.
So, of course, one part of Barclays isn't allowed to talk to the other part. That's called a "Chinese wall". That's enforced by "compliance officers". That works about as well as you'd expect it to - how do compliance officers stop people meeting in the pub after work? In this case, they were even communicating via email and suchlike, and you and I know that a permanent record will be kept of that, to be used in future proceedings. They were so stupid, they couldn't even conspire in secret.
Guess what. Some traders noticed that they could cheat. So they did.
And it isn't just Barclays. Loads of other banks are being investigated for doing the same thing.
Why does that affect us?
Think about the horse race again. If you discover that races you've been betting on, were also bet on by someone who was also influencing the result in a naughty way, you'd be hopping mad, because you've lost money to someone who was cheating. And you'd want to sue someone.
I'd guess that substantial lawsuits are already being prepared, and that's one of the reasons why Barclays share price has dropped so much.
But there's worse.
If you know that horse races are being fixed, you won't want to bet in future. The financial sector in the UK is very important to our economy. And it's just had a big spanner thrown into the works.
I don't think that the reputation of bankers as a breed, had started to recover. The Barclays fiasco hammers another nail into the coffin of bankers' respectability.