Visa and MasterCard are both payment cards and there's no real difference between the two since they're very widely accepted cards around the world.
The only real difference between the Visa and MasterCard is the name and company who manages the payment cards but neither Visa nor MasterCard issue the cards themselves.
Visa and MasterCard are not credit card companies themselves per say because the credit card companies such as Capital One etc are the ones who issue credit cards but use either the Visa or MasterCard company for the payment system.