The word Galop has the usual significance in the most rapid pace of a horse and the word Gallopade referring to a similar movement in dancing, Gallopade is really the correct term. The term Galop came from the Waltz-like turning of the dance, which also has a version called a "Galop-waltz" in 3/4 time.
The origin of the Galop is Hungary (some say Germany). It was often danced after the Volte and the country dances (Contredanses) as a variant to the slow and solemn dances such as the Mazurka. Around 1815, the Galop began to be
recognized socially. It first appeared in Vienna and Berlin about the year 1822, was introduced at the Balls given in France (L.G. Brookes says 1800) by the Duchess de Berri (1798-1870) during the Carnival of 1829 as well as England in that same year. It was rendered famous by its termination of the masked Balls at the French Opera.
The basic Galop has the lead moving forward and the follow backward, no turning in counter-clockwise fashion around the floor. Most Galops were written in 2/4 time and was basically a "Slide, Change, Slide -- Slide, Change, Slide, etc." But!, it is said that the steps resembled a "Valse à deux temps" (waltz.) The couple dance version is done in basic ballroom position and travels counter-clockwise (Line-of-dance) around the floor, Basically consists of a Glissade with one foot and a Chasse', then alternate. This dance can be done as a group dance as well (see clip).
It has been said that there was no dance more exciting, or easy to learn, it required only a good ear to mark the time of the music. The chief requisite in this dance is to keep on one's feet, for there is great danger if once you fall that you will have those who follow over you really following over you... If you get my meaning!
The Galop was often used in classic Ballet's. The Galop is actually the forerunner of the Polka with the Minuet usually followed a Galop and then a Volte in dance order. The Berlin dance was a mix of the Polka and Galop dances.
Modern day we have a few dance steps / movements called "the Gallop" such as Psy's animated riding of a horse in his viral video "Gangnam Style" Song. Another similar is one hand out front and the other occasionally whipping the horses rea end while doing the Gallop motion with the legs, etc. But these have no relation to the original polka type dance of this page.