POS or Point-of-Sale is any device that controls the sale transaction of merchandise.  Orginally they were called cash registers.

All  POS systems, above all else, must provide smooth, efficient service to the customer.  We have all been in situations where it seemed as if it took longer to buy something than it took to get to the store.  Your POS system must work smoothly and hassle-free to make your customers' shopping experience a pleasant one.

The POS system must also be user friendly.  By that we mean that the POS system should have logic built in that allows your cashiers and servers to work competently with a minimum amount of training.

Lastly, you the owner must be able to utilize the POS system to your most profitable end.  You will need to protect yourself from possible theft.  You will want to be PCI compliant.*  You will want to reduce your manual work load by using efficient software for your backoffice reporting.