Final answer:
The practice is referred to as diversion.
Step-by-step explanation:
The practice of luxury perfume brands being diverted from authorized channels for sale at mass-retail outlets is referred to as diversion. Diversion occurs when perfumes are sold outside of the intended distribution channel, which can lead to unauthorized sales and potential counterfeit products entering the market. In the case of Givenchy and Christian Dior's Dune fragrance, their presence in mass-retail outlets may indicate that they have been diverted from their authorized channels of distribution.