What is the role of OLAP in decision - making? What does the term drill mean down in an executive information system

the Short for Online Analytical Processing, a category of software tools that provides analysis of data stored in a database. OLAP tools enable users to analyze different dimensions of multidimensional data. For example, it provides time series and trend analysis views. OLAP often is used in data mining.
The chief component of OLAP is the OLAP server, which sits between a client and a database management systems (DBMS). The OLAP server understands how data is organized in the database and has special functions for analyzing the data. There are OLAP servers available for nearly all the major database systems.

OLAP (online analytical processing) is a function of business intelligence software that enables a user to easily and selectively extract and view data from different points of view. Designed for managers looking to make sense of their corporate data and related information, OLAP tools structure data hierarchically – the way managers think of their enterprises.  But the best OLAP tools also allow business analysts to rotate their views on the information, changing the relationships in order to get more detailed insight into corporate trends and identifiy potential issues and opportunities.

Information Builders' WebFOCUS combines all the functionality of query tools, reporting tools, analytics and OLAP into a single powerful solution with one common interface so business analysts can slice and dice the data and see business processes in a new way. WebFOCUS makes data part of an organization's natural culture by giving developers the premier design environments for automated ad hoc and parameter-driven reporting and giving everyone else the ability to receive and retrieve data in any format, performing analysis using whatever device or application is part of the daily working life.
WebFOCUS ad hoc reporting features allow users to slice and dice data in an almost unlimited number of ways. Satisfying the broadest range of analytical needs, business intelligence application developers can easily enhance reports with extensive data-analysis functionality so that end users can dynamically interact with the information. WebFOCUS also supports the real-time creation of Excel spreadsheets and Excel PivotTables with full styling, drill-downs, and formula capabilities so that Excel power users can analyze their corporate data sources in a tool with which they are already familiar.

A way of viewing related items of a Dimension as defined in a Hierarchy by expanding Members to access a more detailed data range; put simply, this means displaying Child Members associated with a specific Parent Member or Aggregate Member within a defined Hierarchy.

DRILL DOWN/UP
Drilling down or up is a specific analytical technique whereby the user navigates among levels of data ranging from the most summarized (up) to the most detailed (down). The drilling paths may be defined by the hierarchies within dimensions or other relationships that may be dynamic within or between dimensions. For example, when viewing sales data for North America, a drill-down operation in the Region dimension would then display Canada, the eastern United States and the Western United States. A further drill- down on Canada might display Toronto, Vancouver, Montreal, etc.