Can someone offer a primer on it?
You have to look at it from a bank's perspective. When you deposit money in a bank, you think it is still yours. It isn't. When it gets deposited in a bank, the money actually legally becomes a bank asset, and you become an unsecured creditor of the bank.
So when they are talking about a bail in, what they mean is that if a too big to fail bank fails, they will no longer get money from the government (good), but they will get money by taking all the unsecured creditor's money, and converting it to bank stock, at a conversion rate where the unsecured creditor will lose about 99% of the value of their deposit. What you thought was yours, isn't, in one blink of electrons. This is what Cyprus did, and now everyone will do it.
Don't lean on the FDIC for security. They will guarantee up to a certain amount, but that is all. There is no guarantee that you will ever be able to withdraw it. It may just have to stay there forever propping up a bank's balance sheet.
Also, look up hypothecation.
I made the comment that people need to keep their money out of the Matrix by the time this happens. What I mean is that your money needs to be stored in physical form somewhere in the real world, and not even a safe deposit box. Even on a normal day, you do not know where your money really is, because whoever you give your money to will send it around the world while you sleep. When things get bad, they will come for your money, and if it can be accessed electronically, they will get it. And they won't announce they are going to do it, they will just do it.
Funny how banks and governments find neutral synonyms for the word “stealing”. Real funny.