Final answer:
An allusion is an indirect reference in a literary text that calls something to mind without mentioning it explicitly.
Step-by-step explanation:
An allusion is an indirect or implied reference to a person, place, event, or work of literature within a literary text. It is designed to call something to mind without mentioning it explicitly. For example, when a character in a play refers to another character as the 'Einstein of our class,' it is an allusion to the well-known physicist Albert Einstein.