As currently used in information technology, to drill down (verb) is to focus in on something. A drilldown (noun) is the act of focusing in.
The term is sometimes used when referring to moving down through a hierarchy of folders and files in a file system like that of Windows. It may also mean clicking through a series of dropdown menus in a graphical user interface.
Microsoft's Visual Studio Analyzer is said to "provide easy drilldown," possibly meaning that it allows the user to get quickly to a desired function or work unit.
The term drillup is also reported in the multi-dimensional data access query language (MDX), which contains the keywords DRILLDOWNMEMBER and DRILLUPMEMBER as well as TOGGLEDRILLSTATE.