Junk dimension

Junk dimension:

Junk dimension is group of flags which gives us kind of Yes / No or True / False answer. The attributes in junk dimension do not belong to the fact table. Junk dimension contains a unique key to all possible combinations of flags and the generated unique key is used in fact table. 
Junk dimensions are also used for placing attributes like non-generic comments from the fact table. Such attributes might consist of data from an optional comment field when a customer places an order.