"Genre" here means genre fiction https://en.wikipedia.org/wiki/Genre_fiction, the sort of mass-market books like romance, fantasy, science fiction and horror. Compare with literary fiction like classics and poetry. It can be used derogatorily to separate commercial literature from "real" literature since genre fiction were usually printed on cheap trade paperbacks, sold in volume and read for entertainment compared to more serious literary and artistic fiction, but I don't think many people today would make that distinction.