Miriam-Webster's dictionary defines "straw poll," also called a "straw vote," as "an unofficial vote taken (as at a chance gathering) to indicate the relative strength of opposing candidates or issues." It is an unofficial means of testing opinion, and is often used by the two major political parties to internally test their candidates.
The term "straw poll" may come from the act of throwing a piece of straw into the air to see which way it blows. Similarly, straw polls give an imprecise measurement of group opinions. These straw polls are helpful but not always accurate. Among other uses, political parties utilize straw polls to take an unofficial vote of their parties' representatives at political conventions and caucuses. These non-binding votes by delegates can indicate which hopeful candidates may have the most political strength, and which may want to consider dropping out of a political race.
News reporters in 1824 conducted the first straw poll by asking voters who they voted for as they were leaving the polls. The largest straw poll was conducted by the Literary Digest in 1936's presidential election. The poll revealed a landslide victory for Alfred Landon. However, the real votes cast gave Franklin Delano Roosevelt his second term in office, proving the straw poll results wrong.