This describes the amount of equity in comparison to debt or the amount of earnings in comparison to debt. 
You can think of it like a gear box. Leverage in banking is the ratio of lending to equity - just like the larger the gear the more oomph it has. 
Example The trouble was that in the run-up to the global financial crisis a lot of banks did more and more lending without raising any extra equity. They were able to "game" the system, as the Basel Committee says, either by using off-balance-sheet vehicles or through other ruses. In future, there will be global limits on banks' leverage.