Its a financial institute which carries out 3 main functions lending, depositing and burrowing. There is only one main Central bank in a country. there can be a lot of commercial banks in a country.
OBVIOUSLY LESS THAN 100 WORDS......LOL
A bank is a financial institution and a financial intermediary that accepts deposits and channels those deposits into lending activities, either directly or through capital markets. A bank connects customers that have capital deficits to customers with capital surpluses.
This definition is less than 100 words... ^_*
read more http://en.wikipedia.org/wiki/Bank