The theory of how things came to be. This deals with finding the laws of nature that govern how things change. Explanation is related to prediction because if one understands the laws of nature that appear to have caused the current state of affairs, and thus has a good explanation for the current state of affairs, this should allow them to predict future states of affairs.
Beyond explanations that invoke the laws of nature, there are some who wish to find an explanation for nature itself. Specifically, one may ask: What is the explanation for all that is known in the universe? What is the explanation for the laws of nature being the way that they are and not different? These are questions of ultimate explanation.
There are many different approaches to these questions. Some will question whether the laws of nature deserve an explanation. Some will argue that this is beyond the scope of possible knowledge. Some will postulate the existence of God as an explanation for how the universe came into existence.