You're probably referring to splitting in the context of a business transaction. In a business transaction you are defining a group of PurePaths(Transactions) that you want to capture and monitor separately. You are also able to specify measures such as response times that can be tracked for that transaction separately from all the rest (normally because these are of a higher importance).
One thing you define is the 'splitting' measure and this is the criteria that will be used to make something like "sub groups" where you can further breakdown the results of the business transaction so that they can be charted and investigated separately. Here is the documentation page for business transactions: https://www.dynatrace.com/support/doc/appmon/appli...
A good example is a recent question posted here about 'splitting' on the HTTP Response Code of web requests. If you tell the business transaction to split on this response code you will get results like this that you can use:
Does that help?