This was a crusade that took place in 1396 and is seen as the last of the major crusades. This crusade ended in a complete disaster for the crusaders, with Coucy and many other important people being taken prisoner by the Ottomans. Coucy ended up dying in captivity.
The point of this crusade was to relieve pressure from the Muslim Ottomans on Christian Europe. The Ottomans were besieging Nicopolis and many European states worried about what would happen if Nicopolis fell. A crusade was organized to relieve Nicopolis and Coucy (who was perhaps the most respected knight in France) led it.
The crusaders (drawn from various parts of Europe) moved through Germany and down the Danube to Buda. From there they went overland to Nicopolis. The crusade ended as a disaster because of the lack of a command structure and because of the fact that knights tended to want glory and honor. Because of this, no one could control the crusader army. This led to poor tactics on the part of the crusaders, which allowed the Ottomans to defeat them completely.
For a really good account of this crusade, please refer to Barbara Tuchman's A Distant Mirror, which discusses the 14th century with an emphasis on Coucy.