The name of a category to which this gr:ProductOrService, gr:Offering, gr:BusinessEntity, or gr:Location belongs.
Note 1: For products, it is better to add an rdf:type statement referring to a GoodRelations-compliant ontology for vertical industries instead, but if you just have a short text label, gr:category is simpler.
Note 2: You can use greater signs or slashes to informally indicate a category hierarchy, e.g. "restaurants/asian_restaurants" or "cables > usb_cables"