Maturity is the date on which life of financial instrument or transaction come to an end, after which it will cease to exist or must be renewed. The word is usually used for foreign exchange spot, deposits, interest rates, forward transactions, options, bonds and commodity swaps. Some instruments like loans and deposits require repayments of interest and principal at maturity.
Regarding the maturity of deposits, it is date when principal amount is returned to the financier, while interest rate on principal amount is paid on maturity or periodically during the lifetime of deposit. Usually deposits of interbank are instant, containing most euro deposit.
The maturity of fixed income instruments such as bonds is date at which debtor is prerequisite to reimburse the outstanding principal amount and applicable interest rate to the financier. The nonpayment of principal amount and interest at date of maturity negatively affect the credit rating of issuers.
Regarding spot exchange transaction, the maturity date is two business days except USD/CAD transactions, which resolve on next business day. While maturity date of foreign exchange swap or forward is date on which closing exchange of currencies take place, it can be something longer than swap.