It is probably just indicating a series of models. All of the models that begin with a "Z" may have more features than an "S", but it certainly won't be standard among manufacturers. Computer manufacturers do the same thing, HP models all begin with one or two letters and are in a series. Canon for example in their digital cameras uses many different letters in their model numbers. I have a four year old A80 digital camera which was the follow on to the A70. It had a few more updated features. I just bought an A590 IS which is far more recent in that series. Yet, they also have a SD1100 IS model that has similar features, but a different frame and housing. The SD's appear to be a little thinner front to back, more squared off and do not have the rounded protrusion on the right side which I like (the A series has it) to aid in holding the camera.

The company's engineering staff may be able to explain it in more detail.

I have a much older Kodak DC3800 2.1 Megapixel camera, and in this case since Kodak at that time was still making film cameras, I think the DC stood for Digital Camera.

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Thanks to Solar Wings for the special siggy.

Thanks for taking the time to write it.