The two word project management term network loop refers specifically to the specific and particular schedule network path that, the design of its given and scheduled network path, uses the same node or nodes twice. In these cases, the path of the network essentially forms a loop in which, at some point along the oath of the pre-defined network, the path loops back to reconnect and traverse a second time a number of already connected nodes. Network loops provide some tricky issues when it comes to conducting an analysis of the project structure. For example, network loop cannot be analyzed through the use the traditional schedule method of analysis such as the previously defined critical path method. Network loops should be avoided whenever possible as it is highly preferable from an analytic standpoint to have one continuous network path which all schedule events follow. That said, it is possible through careful processing and analysis to successfully utilize network loops on occasion.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.