This is what the dictionary says:
al·lu·sionəˈlo͞oZHən/nounan expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference."an allusion to Shakespeare"synonyms:reference to, mention of, suggestion of, hint to, intimation of, comment on, remark on"the town's name is an allusion to its founding family"the practice of making allusions, especially as an artistic device.
Its something to do with referencing something
