Some of the terminology used for drippers / emitters are listed here.
PC - Stands for Pressure Compensating. This allows for longer single runs of tubing with the dripper giving close to the same flow rate in a wider range of pressures.
Drippers / Emitters - Same thing, just wording.
Check Valve - This feature keeps anything from being siphioned back into the dripper once water is turned off. The ones we sell also keep the lowest in elevation from draining all the water out. Designed for use below ground.
Non-Drip or Anti-Drip - Makes drippers stop flowing once the water is turned off. Designed for use in greenhouses where dripper is above the plants being watered.
Flag - Pretty much the look of the dripper but they can be taken apart for cleaning by turning the flag. Do not come in PC style.