A dynamic template needs to handle your changing needs on the fly. Keep in mind, this isn't magic and it does require some user effort and interaction. But, properly designed, a DRNT can allow for the shuffling of elements or the the substitution of elements for other elements without requiring a full redesign of the template by the user producing the newsletter.
What is dynamic? Again, an example is probably most instructive. Look again at the template from Microsoft Publisher. There is nothing wrong with the template. In fact, it is quite good and could be used to easily publish a newsletter for a small business or other organization.

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Looks great right? Now, let's take a look at next month's newsletter.

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Not bad. We have a new title, new text, new pictures, but, does it look like a fresh newsletter? If you publish a newsletter every month, how long before it starts to get a little stale? Heaven forbid if this is a weekly newsletter.
Now, a solid desktop publishing pro could tweak this layout in a few minutes and have a fresh new look ready to go in no time. But, as a small business owner, you are an expert at running your business. Do you have the time to become an expert at desktop publishing as well? Or, can you afford to keep paying the pro to do it for you?