A credit crunch is a sudden reduction in the availability of loans (or "credit") or a sudden increase in the cost of obtaining a loan from the banks. There are a number of reasons why banks may suddenly increase the costs of borrowing or make borrowing more difficult. This may be due to an anticipated decline in value of the collateral used by the banks when issuing loans, or even an increased perception of risk regarding the solvency of other banks within the banking system. It may be due to a change in monetary conditions (for example, where the central bank suddenly and unexpectedly raises interest rates) or even may be due to the central government imposing direct credit controls or instructing the banks not to engage in further lending activity.