Answer:
Ordinary bikes have a riding position that's either upright or leaning forward, while recumbents have a reclining riding position, some to the point of almost putting the rider on his back. Usually they're heavier than ordinary bikes, but also offer less wind resistance. The weight and the limited ability for the rider to move his body around makes them less suited for climbs and technically challenging rides, while the lower wind resistance makes them an excellent choice for flat rides.