Banks are defined as entities authorized by the Central Bank's Monetary Board to engage in lending funds obtained through deposit accounts. They have four main functions: 1) Depository function, which involves holding deposits for individuals and businesses in accounts like savings, checking, money market, and certificates of deposit. 2) Trust function, where they manage assets for trustors and distribute them to beneficiaries. 3) Collection and remittance of checks, payments, and funds for customers and take a fee for these services. 4) Making loans and providing credit to individuals and businesses, as well as discounting financial instruments.