Answer:
The word "digress" means to turn from the central point of a statement or discourse, to address a minor or secondary point. For example, if discussing coal mining practices, a speaker or writer might "digress" if he began describing detailed problems with a particular mine, or the individuals involved, during the mine's history of use.
Using specific examples to explain general principles is not digression, as it would only occur when the exposition began to concentrate on the example instead.
"But I Digress..."
The stereotypical transition by speakers is "but I digress". This is an abrupt change back to the original central topic.