Dynamic content is assembled when it plays rather than fixed when it was designed. A static asset is a finished file; a dynamic one is a template plus whatever the data says at that moment.
That distinction has practical consequences. One template serves four hundred stores with local prices. A single design covers a whole product range. A change to the underlying data updates every screen without republishing anything, which is the only way a large network stays accurate.
The caveat is that dynamic content cannot be proofread the way a finished file can. You approve a template and a data source, not the thing the customer sees, so the review has to cover the edge cases: the longest product name, a missing image, a price with more digits than the layout expects, a translation that runs 40% longer than the English.
Design the template for the worst case in the data, not the example. Most dynamic-content failures are layout failures (text overflowing, a field collapsing) rather than data failures, and they only appear on the screens nobody is standing in front of.