OPML files are like repositories which are used to keep list of feeds for archive purposes and to subscribe to those feeds later quickly at once.
'Dynamic OPML' files are located on the internet and have dynamically changing list of feeds inside. They are dynamic because of the fact that they are mainly used to present list of favorite feeds, such as list of Top 10 podcasts of this week.
Ziepod is capable of monitoring these dynamic OPML files on the Internet like any other feed and notifying you of those newly added feeds so that you can check those new feeds and subscribe to them as soon as possible.
Dynamic OPML files are represented with ( ) icon and placed under 'My Dynamic OPMLs' folder in the folder hierarchy.