CRR is the fraction of the deposits which commercial banks are required under law to keep as cash reserves, with the central bank. CRR is a powerful instrument to control credit and lending capacity of the banks.
SLR is a part of deposits which Commercial Banks have to keep with themselves. Banks are required to keep a fixed percentage of its assets in cash, gold or other securities. SLR is raised to reduce the ability, of the banks to give credit.
