An ellipsis is a powerful punctuation tool that serves several purposes. When it comes to writing poetry or quoting parts of a poem, ellipses are extremely useful, whether you want to emphasize a point or indicate that you have purposely omitted parts of a quote. Generally speaking, an ellipsis is a series of periods, usually three (...), although there are other variations when you're directly quoting a poem.
The Three-Period Ellipsis
The most common ellipsis consists of three periods. A poem could contain this kind of ellipsis for one of several reasons -- namely a pause, hesitation or unfinished thought. Poets can use this tool to emphasize their point and bring in a more human voice to the piece. Langston Hughes uses this technique in "Dream Variations": "Rest at pale evening . . . / A tall, slim tree . . . / Night coming tenderly / Black like me." When quoting a poem where you purposely want to omit parts of a passage, substitute an ellipsis for the missing parts: "Then rest at cool evening . . . / That is my dream!"
Other Types of Ellipses
Use an ellipsis with four periods when you are directly quoting a poem and omitting the end of a sentence, yet the remaining selection still forms a complete sentence. Here is an example: "To say I'm without fear -- / It wouldn't be true. / I'm afraid of sickness . . . ." A full line of ellipses is used to replace a full line omitted from the poem, as in this quotation from Louise Glück's "Confession":
To say I'm without fear -- It wouldn't be true. . . . . . . . . . . . . . . . . . . . . Like anyone, I have my dreams.