The term Lincoln-Douglas debate comes from the original debates between Abraham Lincoln and Stephen Douglas on the topic of the morality of slavery in 1858. The original debates can be found at http://www.umsl.edu/~virtualstl/dred_scott_case/texts/lindoug.htm.
In the tradition of their namesake, L-D Debate rounds revolve around morality and logic, rather than facts and figures.
LD rounds are generally conducted one on one.