In information technology to drill down means to move from one place to another, information to detailed data by focusing in on something. In a GUI-environment, "drilling-down" may involve clicking on some representation in order to reveal more detail.
To drill down through a series of notebooks, for example, on a desktop means to move through the hierarchy of folders (from the top downwards) to find a specific file or to click through drop-down menus in a GUI. Clicking on an item moves you to a level of greater detail. When an online user accesses more and more pages of the website, he or she may delve deeper into the content of the site. As a web-surfer goes further into a website, he or she goes deeper into the back pages and thus deeper into data. (Of course, he or she could also begin—for example via an external search engine—at a detailed view, and drill up to the front page of the site.)
Drilling down through a database involves accessing information by starting with a general category and moving through the hierarchy: from category to file/table to record to field. When one drills down, one performs de facto data analysis on a parent attribute. Drilling down provides a method of exploring multidimensional data by moving from one level of detail to the next. Drill-down levels depend on the data granularity.
The field of managerial economics uses the term "Drill Down" to explain certain technical aspects of operations research and regression analysis.
For an alternative data-extraction metaphor, see data mining.