A sunroof is opaque (usually flush metal with the body color on the outside). This roof can either tilt open to vent, slide open to let in light, or both. It is called a sunroof because the opacity prevents the sun from heating up the vehicle. These have existed for quite some time.

In the 1970s, Ford introduced a glass sunroof that they named the Moonroof (actually, the American Sunroof Company, the company that made all domestic sunroofs and now known as American Specialty Cars invented it, but Ford was the first to install it). So to answer the question, a moonroof is a sunroof made of glass.
The problem is, the distinction is becoming lost as more and more people use it incorrectly. Most people today just consider any sort of hole in the roof a sunroof. But in the strictest sense, sunroof=metal, moonroof=glass.

Many think that a sunroof is clear and a moonroof is tinted. Nope, not the right answer. Others think that a sunroof will open but a moonroof will not. Wrong again. The truth is that a moonroof is actually a type of sunroof! For more info, I'm deferring to an expert, Marc Levinson of Donmar Sunroofs, who also operates the free sunroof information site.

Here it is: Just as a sedan is a distinctive type of automobile, a moonroof is a type of sunroof. Sunroof is the generic term used to describe any panel in a vehicle roof which can let in light and/or air.
The term moonroof was used in the 70's to describe a glass panel inbuilt electric sunroof, and is now used generically to describe all glass panel inbuilt sunroofs. An inbuilt sunroof is one where the operable panel slides between the vehicle roof and headliner, and is often powered but may be manually operated"

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