Drill down / double click
To go deeper into one part of an analysis for more detail, moving from a summary to specifics. Also called peeling the onion, layer by layer to the root cause.
Also called Double click, Peel the onion
Drill down / double click in practice
Hypothetical: when an owner asks why gross margin is tight, an analyst drills down from the income-statement summary into costs by product line to investigate the question.