What's the difference between a sprocket and a chainring? I'll get a picture or two here, but in a nutshell:
A sprocket connects directly to the crank - a chainring connects to a "spider" or interface that allows it to be "easily" changed.
Usually a Beach Cruiser or a child's bike will have a sprocket. A quality Road Bike or Mountain Bike will have a chainring.
Usually the difference is quality- however, discount store bikes have smeared this distinction as well.