This is what the dictionary says:
al·lu·sion<span>əˈlo͞oZHən/</span>nounan expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference."an allusion to Shakespeare"<span>synonyms:<span>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"</span></span>the practice of making allusions, especially as an artistic device.
Its something to do with referencing something