An allusion is a figure of speech that involves a (generally covert) referrence to something (another text, an object, a circumstance) from another context. Eliot was an extremely literate man, and his poems are filled to the brim with allusions. In "The Love Song of J. Alfred Prufrock" we can find the phrase "And indeed there will be time" twice (lines 23 and 37) which constitutes an allusion to "To His Coy Mistress", a poem by Andrew Marvell that Eliot admired. Marvell's poem questions whether there will be "world enough and time"; Eliot's speaker in this poem answers that "indeed there will be time".