Also: in-depth analysis, or detail view report
With a drill down, information is first analyzed on a global level, after which it is possible to go into depth per component. This can be facilitated in a graphical interface with the option to click on categories or segments, after which a breakdown of the underlying data appears. More detailed information is accessed with each click.
An example of such an in-depth analysis is the content drill down of various web statistics pages (including Google Analytics). Information can be obtained about the number of visitors to individual pages by looking them up in the hierarchical structure of the website. This requires that the website uses logically constructed friendly URLs.
The term is commonly used in the analysis of statistical information, but there are many ways in which a drill down can be performed. For example, a visit to a website, where the visitor clicks on different pages to obtain increasingly targeted information, can also be labeled as a drill down.