Bitcoin (abbreviated BTC) is an electronic payment system in which virtual "money" (bitcoins) is circulating. Do you have VISA or Mastercard plastic cards? Both Visa and MasterCard are also electronic payment systems. However, they use the usual currency - dollars, euro, hryvnia, rubles and all transactions are bank processing. Such currencies are called phiatic. The Bitcoin system uses crypto currency - a purely digital currency that does not have a binding to any global bank or economy of any country. It has its own cost (rate), formed against the backdrop of demand.
Bitcoin solves the dilemma of the need for a trusted third party to control the money supply.