This is the wide, roomy and well-padded bicycle seat that is common to cruiser and utility road bikes. The rider sits in an upright position, and it is not meant for hard pedaling. It is also typically a pretty heavy seat. These maximize comfort over performance, so seeing them on a racing, dirt or mountain bike is pretty unusual.
The basics of a seat for a racing bike should be familiar to anyone who owned a 10-speed as a teenager. It resembles a narrow, rounded triangle, and therefore even looks like something that is meant for slicing through the air. It's light and offers minimum padding, meant to be ridden with the rider bent forward over handlebars that are mounted lower than the seat itself. Proper use of a seat of this kind means that much of the rider's weight is borne by the legs rather than the seat, which is probably why casual riders of a racing-style bike find the seat so uncomfortable. The seat facilitates a lot of pedaling with an eye to achieving a high rpm.
Mountain Bike Seats
It is easy to confuse a racing seat with a mountain bike seat as the two do share some similar characteristics. A mountain biker is also doing a lot of heavy pedaling and also uses his legs more than his butt to bear his weight. However, a mountain biker need to take bumps that a racing cyclist does not, so the seat has extra padding. These seats are also typically larger to facilitate the bumps and also because mountain cyclists are often shifting their weight around during the course of a ride.
Some spins that are often put on the practical seats like those for mountain or racing bikes practically constitute their own type. Cutaway seats, for example, remove the seat center to prevent the rider from sitting on it the wrong way and creating pressure points. Gel seats work by molding themselves into a good fit. Suspension seats offer more support while retaining the lightweight, sporty look of a racing seat.
Leather seats will chafe at first, but they become a pleasure once you break them in. Also just like a fine pair of leather boots, they look great but demand a good deal of care to keep them that way. They resemble a cross between a wide seat and a racing seat. When one remembers that the technical term for a bicycle seat is "saddle," it is perhaps best to think of the classic look of a leather bicycle seat as if it really were, in fact, a saddle, and to take care of it accordingly.