POS - Point of Sale
"Point of Sale" could be called a "computerized" synonym of cash register. In a retail shop it is a physical location, we call a billing counter, where transactions of all your purchases are made.
A Point of Sale terminal tends to be the last point of your shopping journey. A typical POS might include a variety of Input/Output devices like a bar code reader, a computer, printer, magnetic card reader and more commonly a touch screen display.
The computer system contains information relevant to the particular type of industry in which the device is installed. For example, in a retail store the system might store the information of all the products available in the store. A typical POS machine for a restaurant might store the price of all the food items in their menu.
The magnetic card reader is used to read the information of ATM or credit card which could be used to pay the bill. Some banks may change fees for each transaction made through the ATM or credit card.
Apart from billing, POS system also helps in analyzing the sales data, inventory and accountancy.