Guide to Data Warehousing and Business Intelligence
A Data Dimension is a set of data attributes pertaining to something of interest to a business. Dimensions are things like "customers", "products", "stores" and "time".
For users of Data Warehouses, data dimensions are entry points to numeric facts (e.g. sale, profit, revenue) that a business wishes to monitor.
For example, a business might want to know how may blue widgets were sold at a specific store in Los Angeles last month.