A broadside is printed material on a single sheet of inexpensive paper and was the cheapest (and therefore most common) form of printing between the 16th-19th centuries. Often times they were large sheets printed on both sides and folded in half. People would pay as little as a penny for these, which allowed for them to be printed in massive quantities. In the 1660s, England was producing nearly half a million each year. They eventually died out when bound books and newspapers came into play. See the other side of this broadside inside the post..
Images are from the digital library at Duke University.