What's a rogue trader?

Julia Felsenthal explains:

Someone who makes trades that haven't been authorized. Every trader is allowed to take on a certain amount of risk, and if he wants to exceed that value he must get the permission of his supervisors. ("Risk" refers not to the amount of money invested but rather the amount one might expect to lose on a particular gamble given the best available estimate of the odds.) Traders are said to have gone rogue when they've either made investments that are too risky, or invested much more money than they're supposed to. In some cases, unauthorized trading leads to profits, in which case it's less likely to be contested. When it results in a loss, traders often end up having to go even more rogue, doubling down to get out of the red. This can lead to other types of fraud.