A junk dimension is a dimension that contains data with a small number of possible values. The sales order, for example, might have more discrete data (yes-no type values), such as
verification_ind (the value is yes if this order has been verified)
credit_check_flag (indicating whether or not the customer credit status for this order has been checked)
new_customer_ind (the value is yes if this is the first order of a new customer)
web_order_flag (indicating whether or not this order was placed online)
This type of data may often be useful to enhance sales analysis and should be stored in a special type of dimension called junk dimension.
This chapter discusses junk dimensions.