Hyperion Essbase Dimension and Hierarchy

A dimention is nothing but a subject oriented meta data, just like hr section, employees section etc.
 

and the hierarchy is depend on the data source, like "hour glassmodel"

Account dimention
time period dimention
High dense dimention
low dense dimention
low sparse dimention
high sparse dimention
attribute dimentions

Dimensions are like your lookup tables and Hierarchies forms Dimensions. Inside dimensions there exists hierarchies. Example Employee is a dimension , inside Employee dimensions there can be hierarchies such as Directors hierarchy, Managers Hierarchy and employees Hierarchy etc.,,