In settlement management, what's an explosion rule?

Hello.

I'm having some trouble understanding what's an explosion rule. I found out the following definition:

"An explosion rule consists of a source field for which you enter values in the business volume selection criteria of a condition contract and a target field to which the source field is exploded for the selection of the business volume. "

What is it meant by "exploded": that the value entered in the source field is migrated to the target field? Also, if the source field can be found in a condition contract, where is the target field? To this last question, I'd answer: in the settlement document. Lastly, what is it meant by "the selection of the business volume"?