Concept:It refers to the percentage of deposits that banks must keep in liquid assets like government securities.Explanation:As per RBI norms, banks in India must maintain a certain portion of their net demand and time liabilities in the form of liquid assets such as government and approved securities.This mandatory requirement is called the Statutory Liquidity Ratio (SLR).Therefore, maintaining 18% of demand and time liabilities in government and approved securities refers to SLR.Answer:D. Statutory Liquidity Ratio (SLR)