Negative interest on excess reserves

Negative interest on excess reserves means that if banks have more money than they need to keep in the bank, then their bank will actually charge them money for having too much. It's like a fee to encourage them to not just keep the extra money in the bank and let it sit there. Think of it like if you had too much candy in your candy jar at home. You would get in trouble with your parents and they might take away some of the candy. The bank does the same thing, so they don't have too much money sitting around not helping people.