First, let’s define terms.

Dynamic content generally means that pages are generated by some chunk of software by reading data from a database. This is a common design pattern for big catalog style websites.

But no matter how the content gets generated, it still ends up being just plain-ol’ HTML by the time it leaves your web server. What the browsers and search engine spiders see is no more nor less HTML than so-called "static" pages. So the content itself is certainly not a problem — the URLs might be.

To generate the right output, a catalog style site will typically use one or more parameters in the query string. For example, /product.jsp?model=12&color=green&style=7.

Historically, search engines have not liked these complex URLs because they will routinely lead to a (nearly) never-ending sequence of pages. A "plain" URL — one without a query string — tended to have an advantage over complex URLs.

This is not as much of a problem today as it once was, but it is still better to avoid complex URLs. To do so requires the use of a URL rewriting engine like Apache’s mod_rewrite module so it is fairly technical, but once done, a "dynamic" website can be made to look entirely "static".