Dynamic (Server Rendered) websites are those websites that have database connectivity and are interactive in nature. Dynamic sites use server side languages to process requests at the time it’s made and generate a page and its contents in real-time. This means that dynamic websites interact with the user accessing the site and render content depending on the user’s actions or settings.
When a user visits your site, data is passed to the server from the user's browser. When a dynamic site is accessed, pages are generated on-the-fly (or in real-time) to the user based on this data from the visitor. Scripting code analyzed and interpreted on the web server and the resulting HTML is displayed to the visitor's web browser.
Since dynamic websites need to access a database, they can be susceptible to hacking. There are many platforms that are considered “open source”, meaning that the underlying code is done by volunteers around the world. These platforms tend to be more vulnerable than platforms that are run by for-profit companies.
The most common dynamic website platform is WordPress. It’s a hybrid org combining the for-profit (WordPress.com) with open-source (WordPress.org). It’s known for blogging but is used just as often for websites, and online sales. WordPress, and most open source platforms update the software every month or so.