Usury means lending money at exorbitant interest rates. Credit-card companies charging annual interest rates of 29% are guilty of usury, as far as I'm concerned.
A good way to remember the meaning of usury is that you can hear the word use in there. Think of charging too much interest as a way of "using" someone. The sad thing about high interest is that it's always the people who can least afford it who are charged rates so high that it amounts to usury. In the old days, if someone was found guilty of usury, they'd be flogged in the town square. Too bad the credit-card companies can't be dragged out of their holes, because they'd surely get a similar beating.