Point of sale - you've heard the term, used in a variety of contexts. Retail and restaurant management and streamline professionals toss the term around like any other heavy jargon.
POS systems come in all sorts of forms. They can be as simple as a cash drawer hooked up to a computer, or fully integrated solution containing an inventory database, credit card processing, bar code scanning, employee tracking and accounting management.
Point of sale systems are generally composed of hardware: (computer, monitor, cash drawer, bar code scanner, credit card processor, receipt printer, server, etc) and software (Microsoft RMS Retail management system, quickpos, Alohapos, Restaurant Manager, etc).
The point of sale system you choose to use should be compatible with your business model. What works for a hobby store won't work for a pizza restaurant, and what works for a chain establishment won't work for a mom and pop shop. Whatever the size of your business, point of sale gives helps you stay afloat in competitive business markets.