A Category Review is the process in which a retailer assesses the health of a set of products and decides if the assortment of goods should be changed. These are often done on a yearly basis and there is a window of time where brands can present new items or make the case to defend their existing items with a sell story.
Retailers will often cut items that are underperforming in velocity. Retailers often pay close attention to their product mix, so unique offerings that might have lower sales can still be attractive if they are incremental to their set.