Here's two short explanations:
"Because Napoleon remained constantly on the offensive, he was able to employ battlefield plans that exploited a great advantage he held over the ponderous armies of his enemies: initiative. One of his favored attack plans was what he called the manoeuvre sur les derrières, which might be called a "reversed-front" battle. In the reversed-front battle scheme, Napoleon distracted the main part of the enemy army with a small detachment, while the remainder of his troops marched around the flank and took the enemy from the rear in a classic battle of envelopment.*"
* See David Chandler, Dictionary of the Napoleonic Wars (New York: Macmillan, 1979), 178-183; Chandler, Campaigns, 162-164; John R. Elting, Swords Around a Throne: Napoleon's Grande Armee (New York: The Free Press, 1988), 529-531.
"Some enduring forms of manoeuvre are described below. They are not firm rules or schemes: one form of manoeuvre may embrace or develop or be turned into another. Generally their aim is to defeat enemy intentions by the disposition of forces with only the minimum of essential tactical fighting. It is important to relate forms of manoeuvre to the overall objectives they are designed to seek. For example, the classic Napoleonic manoeuvre sur les derrières was usually intended to hold one part of the enemy forces to prevent its concentration and so allow the successive defeat of all the parts in detail. It cannot be divorced from the individual objectives Napoleon sought. However, many followers trying to codify his system ignored this and developed it slavishly into theories, often with disastrous results."