Zero lower bound

Central banks adjust interest rates in their attempts to stimulate or slow down the economy. There is no upper limit to rates but economists debated whether rates could be cut below zero; that is, could depositors be penalised for keeping their money in a bank. However, central banks showed, in the aftermath of the 2007-09 financial crisis, that it was possible to introduce negative interest rates albeit for commercial banks, rather than for individuals. For more, read this article.